Commander: Test Your Command Line interfaces on Windows, Linux and Osx

Commander

Define language independent tests for your command line scripts and programs in simple yaml files.

It runs on windows, osx and linux
It can validate local machines, ssh hosts and docker containers
It is a self-contained binary - no need to install a heavy lib or language
It is easy and fast to write

For more information take a look at the quick start, the examples or the integration tests.

Installation

Any system with Go installed

Probably the easiest way to install commander is by using go get to download and install it in one simple command:

go get github.com/commander-cli/commander/v2/cmd/commander

This works on any OS, as long as go is installed. If go is not installed on your system, follow one of the methods below.

Linux & osx

Visit the release page to get the binary for you system.

curl -L https://github.com/commander-cli/commander/releases/download/v2.5.0/commander-linux-amd64 -o commander
chmod +x commander

Windows

Download the current release
Add the path to your path environment variable
Test it: commander --version

Quick start

A commander test suite consists of a config and tests root element. To start quickly you can use the following examples.

# You can even let commander add tests for you!
$ ./commander add --stdout --file=/tmp/commander.yaml echo hello
tests:
  echo hello:
    exit-code: 0
    stdout: hello

written to /tmp/commander.yaml

# ... and execute!
$ ./commander test /tmp/commander.yaml
Starting test file /tmp/commander.yaml...

✓ echo hello

Duration: 0.002s
Count: 1, Failed: 0

Complete YAML file

Here you can see an example with all features for a quick reference

nodes:
  ssh-host1:
    type: ssh
    addr: 192.168.0.1:22
    user: root
    pass: pass
  ssh-host2:
    type: ssh
    addr: 192.168.0.1:22
    user: root
    identity-file: /home/user/id_rsa.pub
  docker-host1:
    type: docker
    image: alpine:2.4
  docker-host2:
    type: docker
    instance: alpine_instance_1

config: # Config for all executed tests
    dir: /tmp #Set working directory
    env: # Environment variables
        KEY: global
    timeout: 50s # Define a timeout for a command under test
    retries: 2 # Define retries for each test
    nodes:
    - ssh-host1 # define default hosts
    
tests:
    echo hello: # Define command as title
        stdout: hello # Default is to check if it contains the given characters
        exit-code: 0 # Assert exit-code
        
    it should skip:
        command: echo "I should be skipped"
        stdout: I should be skipped
        skip: true
        
    it should fail:
        command: invalid
        stderr:
            contains: 
                - invalid # Assert only contain work
            not-contains:
                - not in there # Validate that a string does not occur in stdout
            exactly: "/bin/sh: 1: invalid: not found"
            line-count: 1 # Assert amount of lines
            lines: # Assert specific lines
                1: "/bin/sh: 1: invalid: not found"
            json:
                object.attr: hello # Make assertions on json objects
            xml:
                "//book//auhtor": Steven King # Make assertions on xml documents
            file: correct-output.txt
        exit-code: 127
        skip: false

    it has configs:
        command: echo hello
        stdout:
            contains: 
              - hello #See test "it should fail"
            exactly: hello
            line-count: 1
        config:
            inherit-env: true # You can inherit the parent shells env variables
            dir: /home/user # Overwrite working dir
            env:
                KEY: local # Overwrite env variable
                ANOTHER: yeah # Add another env variable
            timeout: 1s # Overwrite timeout
            retries: 5
            nodes: # overwrite default nodes
              - docker-host1
              - docker-host2
        exit-code: 0

Executing

# Execute file commander.yaml in current directory
$ ./commander test 

# Execute a specific suite
$ ./commander test /tmp/test.yaml

# Execute a single test
$ ./commander test /tmp/test.yaml --filter "my test"

# Execute suite from stdin
$ cat /tmp/test.yaml | ./commander test -

# Execute suite from url
$ ./commander test https://your-url/commander_test.yaml

# Execute suites within a test directory
$ ./commander test --dir /tmp

# Execute suites in a different working directory 
$ ./commander test --workdir /examples minimal_test.yaml

Adding tests

You can use the add argument if you want to commander to create your tests.

# Add a test to the default commander.yaml
$ ./commander add echo hello
written to /tmp/commander.yaml

# Write to a given file
$ ./commander add --file=test.yaml echo hello
written to test.yaml

# Write to stdout and file
$ ./commander add --stdout echo hello
tests:
  echo hello:
    exit-code: 0
    stdout: hello

written to /tmp/commander.yaml

# Only to stdout
$ ./commander add --stdout --no-file echo hello
tests:
  echo hello:
    exit-code: 0
    stdout: hello

Documentation

Usage

NAME:
   Commander - CLI app testing

USAGE:
   commander [global options] command [command options] [arguments...]

COMMANDS:
     test     Execute the test suite
     add      Automatically add a test to your test suite
     help, h  Shows a list of commands or help for one command

GLOBAL OPTIONS:
   --help, -h     show help
   --version, -v  print the version

Tests

Tests are defined in the tests root element. Every test consists of a command and an expected result, i.e. an exit-code.

tests: # root element
  echo test: # test case - can either be the command or a given title
    stdout: test
    exit-code: 0

A test is a map which configures the test. The key (echo test in the example above) of the test can either be the command itself or the title of the test which will be displayed in the test execution.

If the same command is tested multiple times it is useful to set the title of the test manually and use the command property. Further the title can be useful to describe tests better. See the commander test suite as an example.

name: title or command under test
type: map
default: {}

Examples:

tests:
  echo test: # command and title will be the same
    stdout: test
    exit-code: 0
    
  my title: # custom title
    command: exit 1 # set command manually
    exit-code: 1

command

command is a string containing the command to be tested. Further the command property is automatically parsed from the key if no command property was given.

name: command
type: string
default: can't be empty
notes: Will be parsed from the key if no command property was provided and used as the title too

echo test: # use command as key and title
  exit-code: 0
  
it should print hello world: # use a more descriptive title...
  command: echo hello world  # ... and set the command in the property manually
  stdout: hello world
  exit-code: 0

config

config sets configuration for the test. config can overwrite global configurations.

name: config
type: map
default: {}
notes:
- for more information look at config

echo test:
  config:
    timeout: 5s

exit-code

exit-code is an int type and compares the given code to the exit-code of the given command.

name: exit-code
type: int
default: 0

exit 1: # will pass
  exit-code: 1
exit 0: # will fail
  exit-code: 1

stdout

stdout and stderr allow to make assertions on the output of the command. The type can either be a string or a map of different assertions.

If only a string is provided it will check if the given string is contained in the output.

name: stdout
type: string or map
default:
notes: stderr works the same way

echo test:
  stdout: test # make a contains assertion
  
echo hello world:
  stdout:
    line-count: 1 # assert the amount of lines and use stdout as a map

contains

contains is an array or string. It checks if a string is contained in the output. It is the default if a string is directly assigned to stdout or stderr.

name: contains
type: string or array
default: []
notes: default assertion if directly assigned to stdout or stderr

echo hello world:
  stdout: hello # Default is a contains assertion

echo more output:
  stdout:
    contains:
      - more
      - output

exactly

exactly is a string type which matches the exact output.

name: exactly
type: string
default:

echo test:
  stdout:
    exactly: test

json

json is a map type and allows to parse json documents with a given GJSON syntax to query for specific data. The key represents the query, the value the expected value.

name: json
type: map
default: {}
notes: Syntax taken from GJSON

cat some.json: # print json file to stdout
  name.last: Anderson # assert on name.last, see document below

some.json file:

{
  "name": {"first": "Tom", "last": "Anderson"},
  "age":37,
  "children": ["Sara","Alex","Jack"],
  "fav.movie": "Deer Hunter",
  "friends": [
    {"first": "Dale", "last": "Murphy", "age": 44, "nets": ["ig", "fb", "tw"]},
    {"first": "Roger", "last": "Craig", "age": 68, "nets": ["fb", "tw"]},
    {"first": "Jane", "last": "Murphy", "age": 47, "nets": ["ig", "tw"]}
  ]
}

More examples queries:

"name.last"          >> "Anderson"
"age"                >> 37
"children"           >> ["Sara","Alex","Jack"]
"children.#"         >> 3
"children.1"         >> "Alex"
"child*.2"           >> "Jack"
"c?ildren.0"         >> "Sara"
"fav\.movie"         >> "Deer Hunter"
"friends.#.first"    >> ["Dale","Roger","Jane"]
"friends.1.last"     >> "Craig"

lines

lines is a map which makes exact assertions on a given line by line number.

name: lines
type: map
default: {}
note: starts counting at 1 ;-)

echo test\nline 2:
  stdout:
    lines:
      2: line 2 # asserts only the second line

line-count

line-count asserts the amount of lines printed to the output. If set to 0 this property is ignored.

name: line-count
type: int
default: 0

echo test\nline 2:
  stdout:
    line-count: 2

not-contains

not-contains is a array of elements which are not allowed to be contained in the output. It is the inversion of contains.

name: not-contains
type: array
default: []

echo hello:
  stdout:
    not-contains: bonjour # test passes because bonjour does not occur in the output
 
echo bonjour:
  stdout:
    not-contains: bonjour # test fails because bonjour occurs in the output

xml

xml is a map which allows to query xml documents viá xpath queries. Like the [json][#json] assertion this uses the key of the map as the query parameter to, the value is the expected value.

name: xml
type: map
default: {}
notes: Used library xmlquery

cat some.xml:
  stdout:
    xml:
      //book//author: J. R. R. Tolkien

some.xml file:

<book>
    <author>J. R. R. Tolkien</author>
</book>

file

file is a file path, relative to the working directory that will have its entire contents matched against the command output. Other than reading from a file this works the same as exactly.

The example below will always pass.

output should match file:
  command: cat output.txt
  stdout:
    file: output.txt

stderr

See stdout for more information.

name: stderr
type: string or map
default:
notes: is identical to stdout

# >&2 echos directly to stderr
">&2 echo error": 
  stderr: error
  exit-code: 0

">&2 echo more errors":
  stderr:
    line-count: 1

skip

skip is a boolean type, setting this field to true will skip the test case.

name: skip
type: bool
default: false

echo test:
  stdout: test
  skip: true

Config

You can add configs which will be applied to all tests within a file or just for a specific test case, i.e.:

config:
  dir: /home/root # Set working directory for all tests

tests:
  echo hello:
    config: # Define test specific configs which overwrite global configs
      timeout: 5s
  exit-code: 0

You also have the option to define a separate config file that will be applied globally to all test cases being ran using the --config flag.

The following will set the working directory for all tests that do not explicitly set config.dir in the file config or the test case config. In short, the lowest level config values takes precednce.

./commander test --config foo/bar/my-conifg.yaml foo/bar/test-suite.yaml

# foo/bar/my-conifg.yaml`

config:
  dir: /home/root # Set working directory for all tests

# foo/bar/test-suite.yaml

tests:
  echo hello:
    config: # Define test specific configs which overwrite global configs
      timeout: 5s
  exit-code: 0

dir

dir is a string which sets the current working directory for the command under test. The test will fail if the given directory does not exist.

name: dir
type: string
default: current working dir

dir: /home/root

env

env is a hash-map which is used to set custom env variables. The key represents the variable name and the value setting the value of the env variable.

name: env
type: hash-map
default: {}
notes:
- read env variables with ${PATH}
- overwrites inherited variables, see #inherit-env

env:
  VAR_NAME: my value # Set custom env var
  CURRENT_USER: ${USER} # Set env var and read from current env

inherit-env

inherit-env is a boolean type which allows you to inherit all environment variables from your active shell.

name: inherit-env
type: bool
default: false
notes: If this config is set to true in the global configuration it will be applied for all tests and ignores local test configs.

inherit-env: true

interval

interval is a string type and sets the interval between retries.

name: interval
type: string
default: 0ns
notes:
- valid time units: ns, us, µs, ms, s, m, h
- time string will be evaluated by golang's time package, further reading time/#ParseDuration

interval: 5s # Waits 5 seconds until the next try after a failed test is started

retries

retries is an int type and configures how often a test is allowed to fail until it will be marked as failed for the whole test run.

name: retries
type: int
default: 0
notes: interval can be defined between retry executions

retries: 3 # Test will be executed 3 times or until it succeeds

timeout

timeout is a string type and sets the time a test is allowed to run. The time is parsed from a duration string like 300ms. If a tests exceeds the given timeout the test will fail.

name: timeout
type: string
default: no limit
notes:
- valid time units: ns, us, µs, ms, s, m, h
- time string will be evaluated by golang's time package, further reading time/#ParseDuration

timeout: 600s

Nodes

Commander has the option to execute tests against other hosts, i.e. via ssh.

Available node types are currently:

local, execute tests locally
ssh, execute tests viá ssh
docker, execute tests inside a docker container

nodes: # define nodes in the node section
  ssh-host:
    type: ssh # define the type of the connection 
    user: root # set the user which is used by the connection
    pass: password # set password for authentication
    addr: 192.168.0.100:2222 # target host address
    identity-file: ~/.ssh/id_rsa # auth with private key
tests:
  echo hello:
    config:
      nodes: # define on which host the test should be executed
        - ssh-host
    stdout: hello
    exit-code: 0

You can identify on which node a test failed by inspecting the test output. The [local] and [ssh-host] represent the node name on which the test were executed.

✗ [local] it should test ssh host
✗ [ssh-host] it should fail if env could not be set

local

The local node is the default execution and will be applied if nothing else was configured. It is always pre-configured and available, i.e. if you want to execute tests on a node and locally.

nodes:
  ssh-host:
    addr: 192.168.1.100
    user: ...
tests:
  echo hello:
    config:
      nodes: # will be executed on local and ssh-host
        - ssh-host
        - local
    exit-code: 0

ssh

The ssh node type will execute tests against a configured node using ssh.

Limitations:

The inhereit-env config is disabled for ssh hosts, nevertheless it is possible to set env variables
Private registries are not supported at the moment

nodes: # define nodes in the node section
  ssh-host:
    type: ssh # define the type of the connection 
    user: root # set the user which is used by the connection
    pass: password # set password for authentication
    addr: 192.168.0.100:2222 # target host address
    identity-file: ~/.ssh/id_rsa # auth with private key
tests:
  echo hello:
    config:
      nodes: # define on which host the test should be executed
        - ssh-host
    stdout: hello
    exit-code: 0

docker

The docker node type executes the given command inside a docker container.

Notes: If the default docker registry should be used prefix the container with the registry docker.io/library/

nodes:
  docker-host:
    type: docker
    image: docker.io/library/alpine:3.11.3
    docker-exec-user: 1000 # define the owner of the executed command
    user: user # registry user
    pass: password # registry password, it is recommended to use env variables like $REGISTRY_PASS
config:
  nodes:
    - docker-host
    
tests:
  "id -u":
     stdout: "1001"

Development

See the documentation at development.md

Misc

Heavily inspired by goss.

Similar projects:

Author: Commander-cli
Source Code: https://github.com/commander-cli/commander
License: MIT license

#go #golang #cli #testing #windows #linux

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Commander: Test Your Command Line interfaces on Windows, Linux and Osx

Nigel Uys

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Commander: Test Your Command Line interfaces on Windows, Linux and Osx

Commander

Define language independent tests for your command line scripts and programs in simple yaml files.

It runs on windows, osx and linux
It can validate local machines, ssh hosts and docker containers
It is a self-contained binary - no need to install a heavy lib or language
It is easy and fast to write

For more information take a look at the quick start, the examples or the integration tests.

Installation

Any system with Go installed

Probably the easiest way to install commander is by using go get to download and install it in one simple command:

go get github.com/commander-cli/commander/v2/cmd/commander

This works on any OS, as long as go is installed. If go is not installed on your system, follow one of the methods below.

Linux & osx

Visit the release page to get the binary for you system.

curl -L https://github.com/commander-cli/commander/releases/download/v2.5.0/commander-linux-amd64 -o commander
chmod +x commander

Windows

Download the current release
Add the path to your path environment variable
Test it: commander --version

Quick start

A commander test suite consists of a config and tests root element. To start quickly you can use the following examples.

# You can even let commander add tests for you!
$ ./commander add --stdout --file=/tmp/commander.yaml echo hello
tests:
  echo hello:
    exit-code: 0
    stdout: hello

written to /tmp/commander.yaml

# ... and execute!
$ ./commander test /tmp/commander.yaml
Starting test file /tmp/commander.yaml...

✓ echo hello

Duration: 0.002s
Count: 1, Failed: 0

Complete YAML file

Here you can see an example with all features for a quick reference

nodes:
  ssh-host1:
    type: ssh
    addr: 192.168.0.1:22
    user: root
    pass: pass
  ssh-host2:
    type: ssh
    addr: 192.168.0.1:22
    user: root
    identity-file: /home/user/id_rsa.pub
  docker-host1:
    type: docker
    image: alpine:2.4
  docker-host2:
    type: docker
    instance: alpine_instance_1

config: # Config for all executed tests
    dir: /tmp #Set working directory
    env: # Environment variables
        KEY: global
    timeout: 50s # Define a timeout for a command under test
    retries: 2 # Define retries for each test
    nodes:
    - ssh-host1 # define default hosts
    
tests:
    echo hello: # Define command as title
        stdout: hello # Default is to check if it contains the given characters
        exit-code: 0 # Assert exit-code
        
    it should skip:
        command: echo "I should be skipped"
        stdout: I should be skipped
        skip: true
        
    it should fail:
        command: invalid
        stderr:
            contains: 
                - invalid # Assert only contain work
            not-contains:
                - not in there # Validate that a string does not occur in stdout
            exactly: "/bin/sh: 1: invalid: not found"
            line-count: 1 # Assert amount of lines
            lines: # Assert specific lines
                1: "/bin/sh: 1: invalid: not found"
            json:
                object.attr: hello # Make assertions on json objects
            xml:
                "//book//auhtor": Steven King # Make assertions on xml documents
            file: correct-output.txt
        exit-code: 127
        skip: false

    it has configs:
        command: echo hello
        stdout:
            contains: 
              - hello #See test "it should fail"
            exactly: hello
            line-count: 1
        config:
            inherit-env: true # You can inherit the parent shells env variables
            dir: /home/user # Overwrite working dir
            env:
                KEY: local # Overwrite env variable
                ANOTHER: yeah # Add another env variable
            timeout: 1s # Overwrite timeout
            retries: 5
            nodes: # overwrite default nodes
              - docker-host1
              - docker-host2
        exit-code: 0

Executing

# Execute file commander.yaml in current directory
$ ./commander test 

# Execute a specific suite
$ ./commander test /tmp/test.yaml

# Execute a single test
$ ./commander test /tmp/test.yaml --filter "my test"

# Execute suite from stdin
$ cat /tmp/test.yaml | ./commander test -

# Execute suite from url
$ ./commander test https://your-url/commander_test.yaml

# Execute suites within a test directory
$ ./commander test --dir /tmp

# Execute suites in a different working directory 
$ ./commander test --workdir /examples minimal_test.yaml

Adding tests

You can use the add argument if you want to commander to create your tests.

# Add a test to the default commander.yaml
$ ./commander add echo hello
written to /tmp/commander.yaml

# Write to a given file
$ ./commander add --file=test.yaml echo hello
written to test.yaml

# Write to stdout and file
$ ./commander add --stdout echo hello
tests:
  echo hello:
    exit-code: 0
    stdout: hello

written to /tmp/commander.yaml

# Only to stdout
$ ./commander add --stdout --no-file echo hello
tests:
  echo hello:
    exit-code: 0
    stdout: hello

Documentation

Usage

NAME:
   Commander - CLI app testing

USAGE:
   commander [global options] command [command options] [arguments...]

COMMANDS:
     test     Execute the test suite
     add      Automatically add a test to your test suite
     help, h  Shows a list of commands or help for one command

GLOBAL OPTIONS:
   --help, -h     show help
   --version, -v  print the version

Tests

Tests are defined in the tests root element. Every test consists of a command and an expected result, i.e. an exit-code.

tests: # root element
  echo test: # test case - can either be the command or a given title
    stdout: test
    exit-code: 0

name: title or command under test
type: map
default: {}

Examples:

tests:
  echo test: # command and title will be the same
    stdout: test
    exit-code: 0
    
  my title: # custom title
    command: exit 1 # set command manually
    exit-code: 1

command

command is a string containing the command to be tested. Further the command property is automatically parsed from the key if no command property was given.

name: command
type: string
default: can't be empty
notes: Will be parsed from the key if no command property was provided and used as the title too

echo test: # use command as key and title
  exit-code: 0
  
it should print hello world: # use a more descriptive title...
  command: echo hello world  # ... and set the command in the property manually
  stdout: hello world
  exit-code: 0

config

config sets configuration for the test. config can overwrite global configurations.

name: config
type: map
default: {}
notes:
- for more information look at config

echo test:
  config:
    timeout: 5s

exit-code

exit-code is an int type and compares the given code to the exit-code of the given command.

name: exit-code
type: int
default: 0

exit 1: # will pass
  exit-code: 1
exit 0: # will fail
  exit-code: 1

stdout

stdout and stderr allow to make assertions on the output of the command. The type can either be a string or a map of different assertions.

If only a string is provided it will check if the given string is contained in the output.

name: stdout
type: string or map
default:
notes: stderr works the same way

echo test:
  stdout: test # make a contains assertion
  
echo hello world:
  stdout:
    line-count: 1 # assert the amount of lines and use stdout as a map

contains

contains is an array or string. It checks if a string is contained in the output. It is the default if a string is directly assigned to stdout or stderr.

name: contains
type: string or array
default: []
notes: default assertion if directly assigned to stdout or stderr

echo hello world:
  stdout: hello # Default is a contains assertion

echo more output:
  stdout:
    contains:
      - more
      - output

exactly

exactly is a string type which matches the exact output.

name: exactly
type: string
default:

echo test:
  stdout:
    exactly: test

json

json is a map type and allows to parse json documents with a given GJSON syntax to query for specific data. The key represents the query, the value the expected value.

name: json
type: map
default: {}
notes: Syntax taken from GJSON

cat some.json: # print json file to stdout
  name.last: Anderson # assert on name.last, see document below

some.json file:

{
  "name": {"first": "Tom", "last": "Anderson"},
  "age":37,
  "children": ["Sara","Alex","Jack"],
  "fav.movie": "Deer Hunter",
  "friends": [
    {"first": "Dale", "last": "Murphy", "age": 44, "nets": ["ig", "fb", "tw"]},
    {"first": "Roger", "last": "Craig", "age": 68, "nets": ["fb", "tw"]},
    {"first": "Jane", "last": "Murphy", "age": 47, "nets": ["ig", "tw"]}
  ]
}

More examples queries:

"name.last"          >> "Anderson"
"age"                >> 37
"children"           >> ["Sara","Alex","Jack"]
"children.#"         >> 3
"children.1"         >> "Alex"
"child*.2"           >> "Jack"
"c?ildren.0"         >> "Sara"
"fav\.movie"         >> "Deer Hunter"
"friends.#.first"    >> ["Dale","Roger","Jane"]
"friends.1.last"     >> "Craig"

lines

lines is a map which makes exact assertions on a given line by line number.

name: lines
type: map
default: {}
note: starts counting at 1 ;-)

echo test\nline 2:
  stdout:
    lines:
      2: line 2 # asserts only the second line

line-count

line-count asserts the amount of lines printed to the output. If set to 0 this property is ignored.

name: line-count
type: int
default: 0

echo test\nline 2:
  stdout:
    line-count: 2

not-contains

not-contains is a array of elements which are not allowed to be contained in the output. It is the inversion of contains.

name: not-contains
type: array
default: []

echo hello:
  stdout:
    not-contains: bonjour # test passes because bonjour does not occur in the output
 
echo bonjour:
  stdout:
    not-contains: bonjour # test fails because bonjour occurs in the output

xml

name: xml
type: map
default: {}
notes: Used library xmlquery

cat some.xml:
  stdout:
    xml:
      //book//author: J. R. R. Tolkien

some.xml file:

<book>
    <author>J. R. R. Tolkien</author>
</book>

file

file is a file path, relative to the working directory that will have its entire contents matched against the command output. Other than reading from a file this works the same as exactly.

The example below will always pass.

output should match file:
  command: cat output.txt
  stdout:
    file: output.txt

stderr

See stdout for more information.

name: stderr
type: string or map
default:
notes: is identical to stdout

# >&2 echos directly to stderr
">&2 echo error": 
  stderr: error
  exit-code: 0

">&2 echo more errors":
  stderr:
    line-count: 1

skip

skip is a boolean type, setting this field to true will skip the test case.

name: skip
type: bool
default: false

echo test:
  stdout: test
  skip: true

Config

You can add configs which will be applied to all tests within a file or just for a specific test case, i.e.:

config:
  dir: /home/root # Set working directory for all tests

tests:
  echo hello:
    config: # Define test specific configs which overwrite global configs
      timeout: 5s
  exit-code: 0

You also have the option to define a separate config file that will be applied globally to all test cases being ran using the --config flag.

./commander test --config foo/bar/my-conifg.yaml foo/bar/test-suite.yaml

# foo/bar/my-conifg.yaml`

config:
  dir: /home/root # Set working directory for all tests

# foo/bar/test-suite.yaml

tests:
  echo hello:
    config: # Define test specific configs which overwrite global configs
      timeout: 5s
  exit-code: 0

dir

dir is a string which sets the current working directory for the command under test. The test will fail if the given directory does not exist.

name: dir
type: string
default: current working dir

dir: /home/root

env

env is a hash-map which is used to set custom env variables. The key represents the variable name and the value setting the value of the env variable.

name: env
type: hash-map
default: {}
notes:
- read env variables with ${PATH}
- overwrites inherited variables, see #inherit-env

env:
  VAR_NAME: my value # Set custom env var
  CURRENT_USER: ${USER} # Set env var and read from current env

inherit-env

inherit-env is a boolean type which allows you to inherit all environment variables from your active shell.

name: inherit-env
type: bool
default: false
notes: If this config is set to true in the global configuration it will be applied for all tests and ignores local test configs.

inherit-env: true

interval

interval is a string type and sets the interval between retries.

name: interval
type: string
default: 0ns
notes:
- valid time units: ns, us, µs, ms, s, m, h
- time string will be evaluated by golang's time package, further reading time/#ParseDuration

interval: 5s # Waits 5 seconds until the next try after a failed test is started

retries

retries is an int type and configures how often a test is allowed to fail until it will be marked as failed for the whole test run.

name: retries
type: int
default: 0
notes: interval can be defined between retry executions

retries: 3 # Test will be executed 3 times or until it succeeds

timeout

timeout is a string type and sets the time a test is allowed to run. The time is parsed from a duration string like 300ms. If a tests exceeds the given timeout the test will fail.

name: timeout
type: string
default: no limit
notes:
- valid time units: ns, us, µs, ms, s, m, h
- time string will be evaluated by golang's time package, further reading time/#ParseDuration

timeout: 600s

Nodes

Commander has the option to execute tests against other hosts, i.e. via ssh.

Available node types are currently:

local, execute tests locally
ssh, execute tests viá ssh
docker, execute tests inside a docker container

nodes: # define nodes in the node section
  ssh-host:
    type: ssh # define the type of the connection 
    user: root # set the user which is used by the connection
    pass: password # set password for authentication
    addr: 192.168.0.100:2222 # target host address
    identity-file: ~/.ssh/id_rsa # auth with private key
tests:
  echo hello:
    config:
      nodes: # define on which host the test should be executed
        - ssh-host
    stdout: hello
    exit-code: 0

You can identify on which node a test failed by inspecting the test output. The [local] and [ssh-host] represent the node name on which the test were executed.

✗ [local] it should test ssh host
✗ [ssh-host] it should fail if env could not be set

local

The local node is the default execution and will be applied if nothing else was configured. It is always pre-configured and available, i.e. if you want to execute tests on a node and locally.

nodes:
  ssh-host:
    addr: 192.168.1.100
    user: ...
tests:
  echo hello:
    config:
      nodes: # will be executed on local and ssh-host
        - ssh-host
        - local
    exit-code: 0

ssh

The ssh node type will execute tests against a configured node using ssh.

Limitations:

The inhereit-env config is disabled for ssh hosts, nevertheless it is possible to set env variables
Private registries are not supported at the moment

nodes: # define nodes in the node section
  ssh-host:
    type: ssh # define the type of the connection 
    user: root # set the user which is used by the connection
    pass: password # set password for authentication
    addr: 192.168.0.100:2222 # target host address
    identity-file: ~/.ssh/id_rsa # auth with private key
tests:
  echo hello:
    config:
      nodes: # define on which host the test should be executed
        - ssh-host
    stdout: hello
    exit-code: 0

docker

The docker node type executes the given command inside a docker container.

Notes: If the default docker registry should be used prefix the container with the registry docker.io/library/

nodes:
  docker-host:
    type: docker
    image: docker.io/library/alpine:3.11.3
    docker-exec-user: 1000 # define the owner of the executed command
    user: user # registry user
    pass: password # registry password, it is recommended to use env variables like $REGISTRY_PASS
config:
  nodes:
    - docker-host
    
tests:
  "id -u":
     stdout: "1001"

Development

See the documentation at development.md

Misc

Heavily inspired by goss.

Similar projects:

Author: Commander-cli
Source Code: https://github.com/commander-cli/commander
License: MIT license

#go #golang #cli #testing #windows #linux

Arvilla Medhurst

1661577180

Swift Tips: A Collection Useful Tips for The Swift Language

SwiftTips

The following is a collection of tips I find to be useful when working with the Swift language. More content is available on my Twitter account!

Property Wrappers as Debugging Tools

Property Wrappers allow developers to wrap properties with specific behaviors, that will be seamlessly triggered whenever the properties are accessed.

While their primary use case is to implement business logic within our apps, it's also possible to use Property Wrappers as debugging tools!

For example, we could build a wrapper called @History, that would be added to a property while debugging and would keep track of all the values set to this property.

import Foundation

@propertyWrapper
struct History<Value> {
    private var value: Value
    private(set) var history: [Value] = []

    init(wrappedValue: Value) {
        self.value = wrappedValue
    }
    
    var wrappedValue: Value {
        get { value }

        set {
            history.append(value)
            value = newValue
        }
    }
    
    var projectedValue: Self {
        return self
    }
}

// We can then decorate our business code
// with the `@History` wrapper
struct User {
    @History var name: String = ""
}

var user = User()

// All the existing call sites will still
// compile, without the need for any change
user.name = "John"
user.name = "Jane"

// But now we can also access an history of
// all the previous values!
user.$name.history // ["", "John"]

Localization through `String` interpolation

Swift 5 gave us the possibility to define our own custom String interpolation methods.

This feature can be used to power many use cases, but there is one that is guaranteed to make sense in most projects: localizing user-facing strings.

import Foundation

extension String.StringInterpolation {
    mutating func appendInterpolation(localized key: String, _ args: CVarArg...) {
        let localized = String(format: NSLocalizedString(key, comment: ""), arguments: args)
        appendLiteral(localized)
    }
}


/*
 Let's assume that this is the content of our Localizable.strings:
 
 "welcome.screen.greetings" = "Hello %@!";
 */

let userName = "John"
print("\(localized: "welcome.screen.greetings", userName)") // Hello John!

Implementing pseudo-inheritance between `structs`

If you’ve always wanted to use some kind of inheritance mechanism for your structs, Swift 5.1 is going to make you very happy!

Using the new KeyPath-based dynamic member lookup, you can implement some pseudo-inheritance, where a type inherits the API of another one 🎉

(However, be careful, I’m definitely not advocating inheritance as a go-to solution 🙃)

import Foundation

protocol Inherits {
    associatedtype SuperType
    
    var `super`: SuperType { get }
}

extension Inherits {
    subscript<T>(dynamicMember keyPath: KeyPath<SuperType, T>) -> T {
        return self.`super`[keyPath: keyPath]
    }
}

struct Person {
    let name: String
}

@dynamicMemberLookup
struct User: Inherits {
    let `super`: Person
    
    let login: String
    let password: String
}

let user = User(super: Person(name: "John Appleseed"), login: "Johnny", password: "1234")

user.name // "John Appleseed"
user.login // "Johnny"

Composing `NSAttributedString` through a Function Builder

Swift 5.1 introduced Function Builders: a great tool for building custom DSL syntaxes, like SwiftUI. However, one doesn't need to be building a full-fledged DSL in order to leverage them.

For example, it's possible to write a simple Function Builder, whose job will be to compose together individual instances of NSAttributedString through a nicer syntax than the standard API.

import UIKit

@_functionBuilder
class NSAttributedStringBuilder {
    static func buildBlock(_ components: NSAttributedString...) -> NSAttributedString {
        let result = NSMutableAttributedString(string: "")
        
        return components.reduce(into: result) { (result, current) in result.append(current) }
    }
}

extension NSAttributedString {
    class func composing(@NSAttributedStringBuilder _ parts: () -> NSAttributedString) -> NSAttributedString {
        return parts()
    }
}

let result = NSAttributedString.composing {
    NSAttributedString(string: "Hello",
                       attributes: [.font: UIFont.systemFont(ofSize: 24),
                                    .foregroundColor: UIColor.red])
    NSAttributedString(string: " world!",
                       attributes: [.font: UIFont.systemFont(ofSize: 20),
                                    .foregroundColor: UIColor.orange])
}

Using `switch` and `if` as expressions

Contrary to other languages, like Kotlin, Swift does not allow switch and if to be used as expressions. Meaning that the following code is not valid Swift:

let constant = if condition {
                  someValue
               } else {
                  someOtherValue
               }

A common solution to this problem is to wrap the if or switch statement within a closure, that will then be immediately called. While this approach does manage to achieve the desired goal, it makes for a rather poor syntax.

To avoid the ugly trailing () and improve on the readability, you can define a resultOf function, that will serve the exact same purpose, in a more elegant way.

import Foundation

func resultOf<T>(_ code: () -> T) -> T {
    return code()
}

let randomInt = Int.random(in: 0...3)

let spelledOut: String = resultOf {
    switch randomInt {
    case 0:
        return "Zero"
    case 1:
        return "One"
    case 2:
        return "Two"
    case 3:
        return "Three"
    default:
        return "Out of range"
    }
}

print(spelledOut)

Avoiding double negatives within `guard` statements

A guard statement is a very convenient way for the developer to assert that a condition is met, in order for the execution of the program to keep going.

However, since the body of a guard statement is meant to be executed when the condition evaluates to false, the use of the negation (!) operator within the condition of a guard statement can make the code hard to read, as it becomes a double negative.

A nice trick to avoid such double negatives is to encapsulate the use of the ! operator within a new property or function, whose name does not include a negative.

import Foundation

extension Collection {
    var hasElements: Bool {
        return !isEmpty
    }
}

let array = Bool.random() ? [1, 2, 3] : []

guard array.hasElements else { fatalError("array was empty") }

print(array)

Defining a custom `init` without loosing the compiler-generated one

It's common knowledge for Swift developers that, when you define a struct, the compiler is going to automatically generate a memberwise init for you. That is, unless you also define an init of your own. Because then, the compiler won't generate any memberwise init.

Yet, there are many instances where we might enjoy the opportunity to get both. As it turns out, this goal is quite easy to achieve: you just need to define your own init in an extension rather than inside the type definition itself.

import Foundation

struct Point {
    let x: Int
    let y: Int
}

extension Point {
    init() {
        x = 0
        y = 0
    }
}

let usingDefaultInit = Point(x: 4, y: 3)
let usingCustomInit = Point()

Implementing a namespace through an empty `enum`

Swift does not really have an out-of-the-box support of namespaces. One could argue that a Swift module can be seen as a namespace, but creating a dedicated Framework for this sole purpose can legitimately be regarded as overkill.

Some developers have taken the habit to use a struct which only contains static fields to implement a namespace. While this does the job, it requires us to remember to implement an empty private init(), because it wouldn't make sense for such a struct to be instantiated.

It's actually possible to take this approach one step further, by replacing the struct with an enum. While it might seem weird to have an enum with no case, it's actually a very idiomatic way to declare a type that cannot be instantiated.

import Foundation

enum NumberFormatterProvider {
    static var currencyFormatter: NumberFormatter {
        let formatter = NumberFormatter()
        formatter.numberStyle = .currency
        formatter.roundingIncrement = 0.01
        return formatter
    }
    
    static var decimalFormatter: NumberFormatter {
        let formatter = NumberFormatter()
        formatter.numberStyle = .decimal
        formatter.decimalSeparator = ","
        return formatter
    }
}

NumberFormatterProvider() // ❌ impossible to instantiate by mistake

NumberFormatterProvider.currencyFormatter.string(from: 2.456) // $2.46
NumberFormatterProvider.decimalFormatter.string(from: 2.456) // 2,456

Using `Never` to represent impossible code paths

Never is quite a peculiar type in the Swift Standard Library: it is defined as an empty enum enum Never { }.

While this might seem odd at first glance, it actually yields a very interesting property: it makes it a type that cannot be constructed (i.e. it possesses no instances).

This way, Never can be used as a generic parameter to let the compiler know that a particular feature will not be used.

import Foundation

enum Result<Value, Error> {
    case success(value: Value)
    case failure(error: Error)
}

func willAlwaysSucceed(_ completion: @escaping ((Result<String, Never>) -> Void)) {
    completion(.success(value: "Call was successful"))
}

willAlwaysSucceed( { result in
    switch result {
    case .success(let value):
        print(value)
    // the compiler knows that the `failure` case cannot happen
    // so it doesn't require us to handle it.
    }
})

Providing a default value to a `Decodable` `enum`

Swift's Codable framework does a great job at seamlessly decoding entities from a JSON stream. However, when we integrate web-services, we are sometimes left to deal with JSONs that require behaviors that Codable does not provide out-of-the-box.

For instance, we might have a string-based or integer-based enum, and be required to set it to a default value when the data found in the JSON does not match any of its cases.

We might be tempted to implement this via an extensive switch statement over all the possible cases, but there is a much shorter alternative through the initializer init?(rawValue:):

import Foundation

enum State: String, Decodable {
    case active
    case inactive
    case undefined
    
    init(from decoder: Decoder) throws {
        let container = try decoder.singleValueContainer()
        let decodedString = try container.decode(String.self)
        
        self = State(rawValue: decodedString) ?? .undefined
    }
}

let data = """
["active", "inactive", "foo"]
""".data(using: .utf8)!

let decoded = try! JSONDecoder().decode([State].self, from: data)

print(decoded) // [State.active, State.inactive, State.undefined]

Another lightweight dependency injection through default values for function parameters

Dependency injection boils down to a simple idea: when an object requires a dependency, it shouldn't create it by itself, but instead it should be given a function that does it for him.

Now the great thing with Swift is that, not only can a function take another function as a parameter, but that parameter can also be given a default value.

When you combine both those features, you can end up with a dependency injection pattern that is both lightweight on boilerplate, but also type safe.

import Foundation

protocol Service {
    func call() -> String
}

class ProductionService: Service {
    func call() -> String {
        return "This is the production"
    }
}

class MockService: Service {
    func call() -> String {
        return "This is a mock"
    }
}

typealias Provider<T> = () -> T

class Controller {
    
    let service: Service
    
    init(serviceProvider: Provider<Service> = { return ProductionService() }) {
        self.service = serviceProvider()
    }
    
    func work() {
        print(service.call())
    }
}

let productionController = Controller()
productionController.work() // prints "This is the production"

let mockedController = Controller(serviceProvider: { return MockService() })
mockedController.work() // prints "This is a mock"

Lightweight dependency injection through protocol-oriented programming

Singletons are pretty bad. They make your architecture rigid and tightly coupled, which then results in your code being hard to test and refactor. Instead of using singletons, your code should rely on dependency injection, which is a much more architecturally sound approach.

But singletons are so easy to use, and dependency injection requires us to do extra-work. So maybe, for simple situations, we could find an in-between solution?

One possible solution is to rely on one of Swift's most know features: protocol-oriented programming. Using a protocol, we declare and access our dependency. We then store it in a private singleton, and perform the injection through an extension of said protocol.

This way, our code will indeed be decoupled from its dependency, while at the same time keeping the boilerplate to a minimum.

import Foundation

protocol Formatting {
    var formatter: NumberFormatter { get }
}

private let sharedFormatter: NumberFormatter = {
    let sharedFormatter = NumberFormatter()
    sharedFormatter.numberStyle = .currency
    return sharedFormatter
}()

extension Formatting {
    var formatter: NumberFormatter { return sharedFormatter }
}

class ViewModel: Formatting {
    var displayableAmount: String?
    
    func updateDisplay(to amount: Double) {
        displayableAmount = formatter.string(for: amount)
    }
}

let viewModel = ViewModel()

viewModel.updateDisplay(to: 42000.45)
viewModel.displayableAmount // "$42,000.45"

Getting rid of overabundant `[weak self]` and `guard`

Callbacks are a part of almost all iOS apps, and as frameworks such as RxSwift keep gaining in popularity, they become ever more present in our codebase.

Seasoned Swift developers are aware of the potential memory leaks that @escaping callbacks can produce, so they make real sure to always use [weak self], whenever they need to use self inside such a context. And when they need to have self be non-optional, they then add a guard statement along.

Consequently, this syntax of a [weak self] followed by a guard rapidly tends to appear everywhere in the codebase. The good thing is that, through a little protocol-oriented trick, it's actually possible to get rid of this tedious syntax, without loosing any of its benefits!

import Foundation
import PlaygroundSupport

PlaygroundPage.current.needsIndefiniteExecution = true

protocol Weakifiable: class { }

extension Weakifiable {
    func weakify(_ code: @escaping (Self) -> Void) -> () -> Void {
        return { [weak self] in
            guard let self = self else { return }
            
            code(self)
        }
    }
    
    func weakify<T>(_ code: @escaping (T, Self) -> Void) -> (T) -> Void {
        return { [weak self] arg in
            guard let self = self else { return }
            
            code(arg, self)
        }
    }
}

extension NSObject: Weakifiable { }

class Producer: NSObject {
    
    deinit {
        print("deinit Producer")
    }
    
    private var handler: (Int) -> Void = { _ in }
    
    func register(handler: @escaping (Int) -> Void) {
        self.handler = handler
        
        DispatchQueue.main.asyncAfter(deadline: .now() + 1.0, execute: { self.handler(42) })
    }
}

class Consumer: NSObject {
    
    deinit {
        print("deinit Consumer")
    }
    
    let producer = Producer()
    
    func consume() {
        producer.register(handler: weakify { result, strongSelf in
            strongSelf.handle(result)
        })
    }
    
    private func handle(_ result: Int) {
        print("🎉 \(result)")
    }
}

var consumer: Consumer? = Consumer()

consumer?.consume()

DispatchQueue.main.asyncAfter(deadline: .now() + 2.0, execute: { consumer = nil })

// This code prints:
// 🎉 42
// deinit Consumer
// deinit Producer

Solving callback hell with function composition

Asynchronous functions are a big part of iOS APIs, and most developers are familiar with the challenge they pose when one needs to sequentially call several asynchronous APIs.

This often results in callbacks being nested into one another, a predicament often referred to as callback hell.

Many third-party frameworks are able to tackle this issue, for instance RxSwift or PromiseKit. Yet, for simple instances of the problem, there is no need to use such big guns, as it can actually be solved with simple function composition.

import Foundation

typealias CompletionHandler<Result> = (Result?, Error?) -> Void

infix operator ~>: MultiplicationPrecedence

func ~> <T, U>(_ first: @escaping (CompletionHandler<T>) -> Void, _ second: @escaping (T, CompletionHandler<U>) -> Void) -> (CompletionHandler<U>) -> Void {
    return { completion in
        first({ firstResult, error in
            guard let firstResult = firstResult else { completion(nil, error); return }
            
            second(firstResult, { (secondResult, error) in
                completion(secondResult, error)
            })
        })
    }
}

func ~> <T, U>(_ first: @escaping (CompletionHandler<T>) -> Void, _ transform: @escaping (T) -> U) -> (CompletionHandler<U>) -> Void {
    return { completion in
        first({ result, error in
            guard let result = result else { completion(nil, error); return }
            
            completion(transform(result), nil)
        })
    }
}

func service1(_ completionHandler: CompletionHandler<Int>) {
    completionHandler(42, nil)
}

func service2(arg: String, _ completionHandler: CompletionHandler<String>) {
    completionHandler("🎉 \(arg)", nil)
}

let chainedServices = service1
    ~> { int in return String(int / 2) }
    ~> service2

chainedServices({ result, _ in
    guard let result = result else { return }
    
    print(result) // Prints: 🎉 21
})

Transform an asynchronous function into a synchronous one

Asynchronous functions are a great way to deal with future events without blocking a thread. Yet, there are times where we would like them to behave in exactly such a blocking way.

Think about writing unit tests and using mocked network calls. You will need to add complexity to your test in order to deal with asynchronous functions, whereas synchronous ones would be much easier to manage.

Thanks to Swift proficiency in the functional paradigm, it is possible to write a function whose job is to take an asynchronous function and transform it into a synchronous one.

import Foundation

func makeSynchrone<A, B>(_ asyncFunction: @escaping (A, (B) -> Void) -> Void) -> (A) -> B {
    return { arg in
        let lock = NSRecursiveLock()
        
        var result: B? = nil
        
        asyncFunction(arg) {
            result = $0
            lock.unlock()
        }
        
        lock.lock()
        
        return result!
    }
}

func myAsyncFunction(arg: Int, completionHandler: (String) -> Void) {
    completionHandler("🎉 \(arg)")
}

let syncFunction = makeSynchrone(myAsyncFunction)

print(syncFunction(42)) // prints 🎉 42

Using KeyPaths instead of closures

Closures are a great way to interact with generic APIs, for instance APIs that allow to manipulate data structures through the use of generic functions, such as filter() or sorted().

The annoying part is that closures tend to clutter your code with many instances of {, } and $0, which can quickly undermine its readably.

A nice alternative for a cleaner syntax is to use a KeyPath instead of a closure, along with an operator that will deal with transforming the provided KeyPath in a closure.

import Foundation

prefix operator ^

prefix func ^ <Element, Attribute>(_ keyPath: KeyPath<Element, Attribute>) -> (Element) -> Attribute {
    return { element in element[keyPath: keyPath] }
}

struct MyData {
    let int: Int
    let string: String
}

let data = [MyData(int: 2, string: "Foo"), MyData(int: 4, string: "Bar")]

data.map(^\.int) // [2, 4]
data.map(^\.string) // ["Foo", "Bar"]

Bringing some type-safety to a `userInfo` `Dictionary`

Many iOS APIs still rely on a userInfo Dictionary to handle use-case specific data. This Dictionary usually stores untyped values, and is declared as follows: [String: Any] (or sometimes [AnyHashable: Any].

Retrieving data from such a structure will involve some conditional casting (via the as? operator), which is prone to both errors and repetitions. Yet, by introducing a custom subscript, it's possible to encapsulate all the tedious logic, and end-up with an easier and more robust API.

import Foundation

typealias TypedUserInfoKey<T> = (key: String, type: T.Type)

extension Dictionary where Key == String, Value == Any {
    subscript<T>(_ typedKey: TypedUserInfoKey<T>) -> T? {
        return self[typedKey.key] as? T
    }
}

let userInfo: [String : Any] = ["Foo": 4, "Bar": "forty-two"]

let integerTypedKey = TypedUserInfoKey(key: "Foo", type: Int.self)
let intValue = userInfo[integerTypedKey] // returns 4
type(of: intValue) // returns Int?

let stringTypedKey = TypedUserInfoKey(key: "Bar", type: String.self)
let stringValue = userInfo[stringTypedKey] // returns "forty-two"
type(of: stringValue) // returns String?

Lightweight data-binding for an MVVM implementation

MVVM is a great pattern to separate business logic from presentation logic. The main challenge to make it work, is to define a mechanism for the presentation layer to be notified of model updates.

RxSwift is a perfect choice to solve such a problem. Yet, some developers don't feel confortable with leveraging a third-party library for such a central part of their architecture.

For those situation, it's possible to define a lightweight Variable type, that will make the MVVM pattern very easy to use!

import Foundation

class Variable<Value> {
    var value: Value {
        didSet {
            onUpdate?(value)
        }
    }
    
    var onUpdate: ((Value) -> Void)? {
        didSet {
            onUpdate?(value)
        }
    }
    
    init(_ value: Value, _ onUpdate: ((Value) -> Void)? = nil) {
        self.value = value
        self.onUpdate = onUpdate
        self.onUpdate?(value)
    }
}

let variable: Variable<String?> = Variable(nil)

variable.onUpdate = { data in
    if let data = data {
        print(data)
    }
}

variable.value = "Foo"
variable.value = "Bar"

// prints:
// Foo
// Bar

Using `typealias` to its fullest

The keyword typealias allows developers to give a new name to an already existing type. For instance, Swift defines Void as a typealias of (), the empty tuple.

But a less known feature of this mechanism is that it allows to assign concrete types for generic parameters, or to rename them. This can help make the semantics of generic types much clearer, when used in specific use cases.

import Foundation

enum Either<Left, Right> {
    case left(Left)
    case right(Right)
}

typealias Result<Value> = Either<Value, Error>

typealias IntOrString = Either<Int, String>

Writing an interruptible overload of `forEach`

Iterating through objects via the forEach(_:) method is a great alternative to the classic for loop, as it allows our code to be completely oblivious of the iteration logic. One limitation, however, is that forEach(_:) does not allow to stop the iteration midway.

Taking inspiration from the Objective-C implementation, we can write an overload that will allow the developer to stop the iteration, if needed.

import Foundation

extension Sequence {
    func forEach(_ body: (Element, _ stop: inout Bool) throws -> Void) rethrows {
        var stop = false
        for element in self {
            try body(element, &stop)
            
            if stop {
                return
            }
        }
    }
}

["Foo", "Bar", "FooBar"].forEach { element, stop in
    print(element)
    stop = (element == "Bar")
}

// Prints:
// Foo
// Bar

Optimizing the use of `reduce()`

Functional programing is a great way to simplify a codebase. For instance, reduce is an alternative to the classic for loop, without most the boilerplate. Unfortunately, simplicity often comes at the price of performance.

Consider that you want to remove duplicate values from a Sequence. While reduce() is a perfectly fine way to express this computation, the performance will be sub optimal, because of all the unnecessary Array copying that will happen every time its closure gets called.

That's when reduce(into:_:) comes into play. This version of reduce leverages the capacities of copy-on-write type (such as Array or Dictionnary) in order to avoid unnecessary copying, which results in a great performance boost.

import Foundation

func time(averagedExecutions: Int = 1, _ code: () -> Void) {
    let start = Date()
    for _ in 0..<averagedExecutions { code() }
    let end = Date()
    
    let duration = end.timeIntervalSince(start) / Double(averagedExecutions)
    
    print("time: \(duration)")
}

let data = (1...1_000).map { _ in Int(arc4random_uniform(256)) }


// runs in 0.63s
time {
    let noDuplicates: [Int] = data.reduce([], { $0.contains($1) ? $0 : $0 + [$1] })
}

// runs in 0.15s
time {
    let noDuplicates: [Int] = data.reduce(into: [], { if !$0.contains($1) { $0.append($1) } } )
}

Avoiding hardcoded reuse identifiers

UI components such as UITableView and UICollectionView rely on reuse identifiers in order to efficiently recycle the views they display. Often, those reuse identifiers take the form of a static hardcoded String, that will be used for every instance of their class.

Through protocol-oriented programing, it's possible to avoid those hardcoded values, and instead use the name of the type as a reuse identifier.

import Foundation
import UIKit

protocol Reusable {
    static var reuseIdentifier: String { get }
}

extension Reusable {
    static var reuseIdentifier: String {
        return String(describing: self)
    }
}

extension UITableViewCell: Reusable { }

extension UITableView {
    func register<T: UITableViewCell>(_ class: T.Type) {
        register(`class`, forCellReuseIdentifier: T.reuseIdentifier)
    }
    func dequeueReusableCell<T: UITableViewCell>(for indexPath: IndexPath) -> T {
        return dequeueReusableCell(withIdentifier: T.reuseIdentifier, for: indexPath) as! T
    }
}

class MyCell: UITableViewCell { }

let tableView = UITableView()

tableView.register(MyCell.self)
let myCell: MyCell = tableView.dequeueReusableCell(for: [0, 0])

Defining a union type

The C language has a construct called union, that allows a single variable to hold values from different types. While Swift does not provide such a construct, it provides enums with associated values, which allows us to define a type called Either that implements a union of two types.

import Foundation

enum Either<A, B> {
    case left(A)
    case right(B)
    
    func either(ifLeft: ((A) -> Void)? = nil, ifRight: ((B) -> Void)? = nil) {
        switch self {
        case let .left(a):
            ifLeft?(a)
        case let .right(b):
            ifRight?(b)
        }
    }
}

extension Bool { static func random() -> Bool { return arc4random_uniform(2) == 0 } }

var intOrString: Either<Int, String> = Bool.random() ? .left(2) : .right("Foo")

intOrString.either(ifLeft: { print($0 + 1) }, ifRight: { print($0 + "Bar") })

If you're interested by this kind of data structure, I strongly recommend that you learn more about Algebraic Data Types.

Asserting that classes have associated NIBs and vice-versa

Most of the time, when we create a .xib file, we give it the same name as its associated class. From that, if we later refactor our code and rename such a class, we run the risk of forgetting to rename the associated .xib.

While the error will often be easy to catch, if the .xib is used in a remote section of its app, it might go unnoticed for sometime. Fortunately it's possible to build custom test predicates that will assert that 1) for a given class, there exists a .nib with the same name in a given Bundle, 2) for all the .nib in a given Bundle, there exists a class with the same name.

import XCTest

public func XCTAssertClassHasNib(_ class: AnyClass, bundle: Bundle, file: StaticString = #file, line: UInt = #line) {
    let associatedNibURL = bundle.url(forResource: String(describing: `class`), withExtension: "nib")
    
    XCTAssertNotNil(associatedNibURL, "Class \"\(`class`)\" has no associated nib file", file: file, line: line)
}

public func XCTAssertNibHaveClasses(_ bundle: Bundle, file: StaticString = #file, line: UInt = #line) {
    guard let bundleName = bundle.infoDictionary?["CFBundleName"] as? String,
        let basePath = bundle.resourcePath,
        let enumerator = FileManager.default.enumerator(at: URL(fileURLWithPath: basePath),
                                                    includingPropertiesForKeys: nil,
                                                    options: [.skipsHiddenFiles, .skipsSubdirectoryDescendants]) else { return }
    
    var nibFilesURLs = [URL]()
    
    for case let fileURL as URL in enumerator {
        if fileURL.pathExtension.uppercased() == "NIB" {
            nibFilesURLs.append(fileURL)
        }
    }
    
    nibFilesURLs.map { $0.lastPathComponent }
        .compactMap { $0.split(separator: ".").first }
        .map { String($0) }
        .forEach {
            let associatedClass: AnyClass? = bundle.classNamed("\(bundleName).\($0)")
            
            XCTAssertNotNil(associatedClass, "File \"\($0).nib\" has no associated class", file: file, line: line)
        }
}

XCTAssertClassHasNib(MyFirstTableViewCell.self, bundle: Bundle(for: AppDelegate.self))
XCTAssertClassHasNib(MySecondTableViewCell.self, bundle: Bundle(for: AppDelegate.self))
        
XCTAssertNibHaveClasses(Bundle(for: AppDelegate.self))

Many thanks Benjamin Lavialle for coming up with the idea behind the second test predicate.

Small footprint type-erasing with functions

Seasoned Swift developers know it: a protocol with associated type (PAT) "can only be used as a generic constraint because it has Self or associated type requirements". When we really need to use a PAT to type a variable, the goto workaround is to use a type-erased wrapper.

While this solution works perfectly, it requires a fair amount of boilerplate code. In instances where we are only interested in exposing one particular function of the PAT, a shorter approach using function types is possible.

import Foundation
import UIKit

protocol Configurable {
    associatedtype Model
    
    func configure(with model: Model)
}

typealias Configurator<Model> = (Model) -> ()

extension UILabel: Configurable {
    func configure(with model: String) {
        self.text = model
    }
}

let label = UILabel()
let configurator: Configurator<String> = label.configure

configurator("Foo")

label.text // "Foo"

Performing animations sequentially

UIKit exposes a very powerful and simple API to perform view animations. However, this API can become a little bit quirky to use when we want to perform animations sequentially, because it involves nesting closure within one another, which produces notoriously hard to maintain code.

Nonetheless, it's possible to define a rather simple class, that will expose a really nicer API for this particular use case 👌

import Foundation
import UIKit

class AnimationSequence {
    typealias Animations = () -> Void
    
    private let current: Animations
    private let duration: TimeInterval
    private var next: AnimationSequence? = nil
    
    init(animations: @escaping Animations, duration: TimeInterval) {
        self.current = animations
        self.duration = duration
    }
    
    @discardableResult func append(animations: @escaping Animations, duration: TimeInterval) -> AnimationSequence {
        var lastAnimation = self
        while let nextAnimation = lastAnimation.next {
            lastAnimation = nextAnimation
        }
        lastAnimation.next = AnimationSequence(animations: animations, duration: duration)
        return self
    }
    
    func run() {
        UIView.animate(withDuration: duration, animations: current, completion: { finished in
            if finished, let next = self.next {
                next.run()
            }
        })
    }
}

var firstView = UIView()
var secondView = UIView()

firstView.alpha = 0
secondView.alpha = 0

AnimationSequence(animations: { firstView.alpha = 1.0 }, duration: 1)
            .append(animations: { secondView.alpha = 1.0 }, duration: 0.5)
            .append(animations: { firstView.alpha = 0.0 }, duration: 2.0)
            .run()

Debouncing a function call

Debouncing is a very useful tool when dealing with UI inputs. Consider a search bar, whose content is used to query an API. It wouldn't make sense to perform a request for every character the user is typing, because as soon as a new character is entered, the result of the previous request has become irrelevant.

Instead, our code will perform much better if we "debounce" the API call, meaning that we will wait until some delay has passed, without the input being modified, before actually performing the call.

import Foundation

func debounced(delay: TimeInterval, queue: DispatchQueue = .main, action: @escaping (() -> Void)) -> () -> Void {
    var workItem: DispatchWorkItem?
    
    return {
        workItem?.cancel()
        workItem = DispatchWorkItem(block: action)
        queue.asyncAfter(deadline: .now() + delay, execute: workItem!)
    }
}

let debouncedPrint = debounced(delay: 1.0) { print("Action performed!") }

debouncedPrint()
debouncedPrint()
debouncedPrint()

// After a 1 second delay, this gets
// printed only once to the console:

// Action performed!

Providing useful operators for `Optional` booleans

When we need to apply the standard boolean operators to Optional booleans, we often end up with a syntax unnecessarily crowded with unwrapping operations. By taking a cue from the world of three-valued logics, we can define a couple operators that make working with Bool? values much nicer.

import Foundation

func && (lhs: Bool?, rhs: Bool?) -> Bool? {
    switch (lhs, rhs) {
    case (false, _), (_, false):
        return false
    case let (unwrapLhs?, unwrapRhs?):
        return unwrapLhs && unwrapRhs
    default:
        return nil
    }
}

func || (lhs: Bool?, rhs: Bool?) -> Bool? {
    switch (lhs, rhs) {
    case (true, _), (_, true):
        return true
    case let (unwrapLhs?, unwrapRhs?):
        return unwrapLhs || unwrapRhs
    default:
        return nil
    }
}

false && nil // false
true && nil // nil
[true, nil, false].reduce(true, &&) // false

nil || true // true
nil || false // nil
[true, nil, false].reduce(false, ||) // true

Removing duplicate values from a `Sequence`

Transforming a Sequence in order to remove all the duplicate values it contains is a classic use case. To implement it, one could be tempted to transform the Sequence into a Set, then back to an Array. The downside with this approach is that it will not preserve the order of the sequence, which can definitely be a dealbreaker. Using reduce() it is possible to provide a concise implementation that preserves ordering:

import Foundation

extension Sequence where Element: Equatable {
    func duplicatesRemoved() -> [Element] {
        return reduce([], { $0.contains($1) ? $0 : $0 + [$1] })
    }
}

let data = [2, 5, 2, 3, 6, 5, 2]

data.duplicatesRemoved() // [2, 5, 3, 6]

Shorter syntax to deal with optional strings

Optional strings are very common in Swift code, for instance many objects from UIKit expose the text they display as a String?. Many times you will need to manipulate this data as an unwrapped String, with a default value set to the empty string for nil cases.

While the nil-coalescing operator (e.g. ??) is a perfectly fine way to a achieve this goal, defining a computed variable like orEmpty can help a lot in cleaning the syntax.

import Foundation
import UIKit

extension Optional where Wrapped == String {
    var orEmpty: String {
        switch self {
        case .some(let value):
            return value
        case .none:
            return ""
        }
    }
}

func doesNotWorkWithOptionalString(_ param: String) {
    // do something with `param`
}

let label = UILabel()
label.text = "This is some text."

doesNotWorkWithOptionalString(label.text.orEmpty)

Encapsulating background computation and UI update

Every seasoned iOS developers knows it: objects from UIKit can only be accessed from the main thread. Any attempt to access them from a background thread is a guaranteed crash.

Still, running a costly computation on the background, and then using it to update the UI can be a common pattern.

In such cases you can rely on asyncUI to encapsulate all the boilerplate code.

import Foundation
import UIKit

func asyncUI<T>(_ computation: @autoclosure @escaping () -> T, qos: DispatchQoS.QoSClass = .userInitiated, _ completion: @escaping (T) -> Void) {
    DispatchQueue.global(qos: qos).async {
        let value = computation()
        DispatchQueue.main.async {
            completion(value)
        }
    }
}

let label = UILabel()

func costlyComputation() -> Int { return (0..<10_000).reduce(0, +) }

asyncUI(costlyComputation()) { value in
    label.text = "\(value)"
}

Retrieving all the necessary data to build a debug view

A debug view, from which any controller of an app can be instantiated and pushed on the navigation stack, has the potential to bring some real value to a development process. A requirement to build such a view is to have a list of all the classes from a given Bundle that inherit from UIViewController. With the following extension, retrieving this list becomes a piece of cake 🍰

import Foundation
import UIKit
import ObjectiveC

extension Bundle {
    func viewControllerTypes() -> [UIViewController.Type] {
        guard let bundlePath = self.executablePath else { return [] }
        
        var size: UInt32 = 0
        var rawClassNames: UnsafeMutablePointer<UnsafePointer<Int8>>!
        var parsedClassNames = [String]()
        
        rawClassNames = objc_copyClassNamesForImage(bundlePath, &size)
        
        for index in 0..<size {
            let className = rawClassNames[Int(index)]
            
            if let name = NSString.init(utf8String:className) as String?,
                NSClassFromString(name) is UIViewController.Type {
                parsedClassNames.append(name)
            }
        }
        
        return parsedClassNames
            .sorted()
            .compactMap { NSClassFromString($0) as? UIViewController.Type }
    }
}

// Fetch all view controller types in UIKit
Bundle(for: UIViewController.self).viewControllerTypes()

I share the credit for this tip with Benoît Caron.

Defining a function to map over dictionaries

Update As it turns out, map is actually a really bad name for this function, because it does not preserve composition of transformations, a property that is required to fit the definition of a real map function.

Surprisingly enough, the standard library doesn't define a map() function for dictionaries that allows to map both keys and values into a new Dictionary. Nevertheless, such a function can be helpful, for instance when converting data across different frameworks.

import Foundation

extension Dictionary {
    func map<T: Hashable, U>(_ transform: (Key, Value) throws -> (T, U)) rethrows -> [T: U] {
        var result: [T: U] = [:]
        
        for (key, value) in self {
            let (transformedKey, transformedValue) = try transform(key, value)
            result[transformedKey] = transformedValue
        }
        
        return result
    }
}

let data = [0: 5, 1: 6, 2: 7]
data.map { ("\($0)", $1 * $1) } // ["2": 49, "0": 25, "1": 36]

A shorter syntax to remove `nil` values

Swift provides the function compactMap(), that can be used to remove nil values from a Sequence of optionals when calling it with an argument that just returns its parameter (i.e. compactMap { $0 }). Still, for such use cases it would be nice to get rid of the trailing closure.

The implementation isn't as straightforward as your usual extension, but once it has been written, the call site definitely gets cleaner 👌

import Foundation

protocol OptionalConvertible {
    associatedtype Wrapped
    func asOptional() -> Wrapped?
}

extension Optional: OptionalConvertible {
    func asOptional() -> Wrapped? {
        return self
    }
}

extension Sequence where Element: OptionalConvertible {
    func compacted() -> [Element.Wrapped] {
        return compactMap { $0.asOptional() }
    }
}

let data = [nil, 1, 2, nil, 3, 5, nil, 8, nil]
data.compacted() // [1, 2, 3, 5, 8]

Dealing with expirable values

It might happen that your code has to deal with values that come with an expiration date. In a game, it could be a score multiplier that will only last for 30 seconds. Or it could be an authentication token for an API, with a 15 minutes lifespan. In both instances you can rely on the type Expirable to encapsulate the expiration logic.

import Foundation

struct Expirable<T> {
    private var innerValue: T
    private(set) var expirationDate: Date
    
    var value: T? {
        return hasExpired() ? nil : innerValue
    }
    
    init(value: T, expirationDate: Date) {
        self.innerValue = value
        self.expirationDate = expirationDate
    }
    
    init(value: T, duration: Double) {
        self.innerValue = value
        self.expirationDate = Date().addingTimeInterval(duration)
    }
    
    func hasExpired() -> Bool {
        return expirationDate < Date()
    }
}

let expirable = Expirable(value: 42, duration: 3)

sleep(2)
expirable.value // 42
sleep(2)
expirable.value // nil

I share the credit for this tip with Benoît Caron.

Using parallelism to speed-up `map()`

Almost all Apple devices able to run Swift code are powered by a multi-core CPU, consequently making a good use of parallelism is a great way to improve code performance. map() is a perfect candidate for such an optimization, because it is almost trivial to define a parallel implementation.

import Foundation

extension Array {
    func parallelMap<T>(_ transform: (Element) -> T) -> [T] {
        let res = UnsafeMutablePointer<T>.allocate(capacity: count)
        
        DispatchQueue.concurrentPerform(iterations: count) { i in
            res[i] = transform(self[i])
        }
        
        let finalResult = Array<T>(UnsafeBufferPointer(start: res, count: count))
        res.deallocate(capacity: count)
        
        return finalResult
    }
}

let array = (0..<1_000).map { $0 }

func work(_ n: Int) -> Int {
    return (0..<n).reduce(0, +)
}

array.parallelMap { work($0) }

🚨 Make sure to only use parallelMap() when the transform function actually performs some costly computations. Otherwise performances will be systematically slower than using map(), because of the multithreading overhead.

Measuring execution time with minimum boilerplate

During development of a feature that performs some heavy computations, it can be helpful to measure just how much time a chunk of code takes to run. The time() function is a nice tool for this purpose, because of how simple it is to add and then to remove when it is no longer needed.

import Foundation

func time(averagedExecutions: Int = 1, _ code: () -> Void) {
    let start = Date()
    for _ in 0..<averagedExecutions { code() }
    let end = Date()
    
    let duration = end.timeIntervalSince(start) / Double(averagedExecutions)
    
    print("time: \(duration)")
}

time {
    (0...10_000).map { $0 * $0 }
}
// time: 0.183973908424377

Running two pieces of code in parallel

Concurrency is definitely one of those topics were the right encapsulation bears the potential to make your life so much easier. For instance, with this piece of code you can easily launch two computations in parallel, and have the results returned in a tuple.

import Foundation

func parallel<T, U>(_ left: @autoclosure () -> T, _ right: @autoclosure () -> U) -> (T, U) {
    var leftRes: T?
    var rightRes: U?
    
    DispatchQueue.concurrentPerform(iterations: 2, execute: { id in
        if id == 0 {
            leftRes = left()
        } else {
            rightRes = right()
        }
    })
    
    return (leftRes!, rightRes!)
}

let values = (1...100_000).map { $0 }

let results = parallel(values.map { $0 * $0 }, values.reduce(0, +))

Making good use of #file, #line and #function

Swift exposes three special variables #file, #line and #function, that are respectively set to the name of the current file, line and function. Those variables become very useful when writing custom logging functions or test predicates.

import Foundation

func log(_ message: String, _ file: String = #file, _ line: Int = #line, _ function: String = #function) {
    print("[\(file):\(line)] \(function) - \(message)")
}

func foo() {
    log("Hello world!")
}

foo() // [MyPlayground.playground:8] foo() - Hello world!

Comparing Optionals through Conditional Conformance

Swift 4.1 has introduced a new feature called Conditional Conformance, which allows a type to implement a protocol only when its generic type also does.

With this addition it becomes easy to let Optional implement Comparable only when Wrapped also implements Comparable:

import Foundation

extension Optional: Comparable where Wrapped: Comparable {
    public static func < (lhs: Optional, rhs: Optional) -> Bool {
        switch (lhs, rhs) {
        case let (lhs?, rhs?):
            return lhs < rhs
        case (nil, _?):
            return true // anything is greater than nil
        case (_?, nil):
            return false // nil in smaller than anything
        case (nil, nil):
            return true // nil is not smaller than itself
        }
    }
}

let data: [Int?] = [8, 4, 3, nil, 12, 4, 2, nil, -5]
data.sorted() // [nil, nil, Optional(-5), Optional(2), Optional(3), Optional(4), Optional(4), Optional(8), Optional(12)]

Safely subscripting a Collection

Any attempt to access an Array beyond its bounds will result in a crash. While it's possible to write conditions such as if index < array.count { array[index] } in order to prevent such crashes, this approach will rapidly become cumbersome.

A great thing is that this condition can be encapsulated in a custom subscript that will work on any Collection:

import Foundation

extension Collection {
    subscript (safe index: Index) -> Element? {
        return indices.contains(index) ? self[index] : nil
    }
}

let data = [1, 3, 4]

data[safe: 1] // Optional(3)
data[safe: 10] // nil

Easier String slicing using ranges

Subscripting a string with a range can be very cumbersome in Swift 4. Let's face it, no one wants to write lines like someString[index(startIndex, offsetBy: 0)..<index(startIndex, offsetBy: 10)] on a regular basis.

Luckily, with the addition of one clever extension, strings can be sliced as easily as arrays 🎉

import Foundation

extension String {
    public subscript(value: CountableClosedRange<Int>) -> Substring {
        get {
            return self[index(startIndex, offsetBy: value.lowerBound)...index(startIndex, offsetBy: value.upperBound)]
        }
    }
    
    public subscript(value: CountableRange<Int>) -> Substring {
        get {
            return self[index(startIndex, offsetBy: value.lowerBound)..<index(startIndex, offsetBy: value.upperBound)]
        }
    }
    
    public subscript(value: PartialRangeUpTo<Int>) -> Substring {
        get {
            return self[..<index(startIndex, offsetBy: value.upperBound)]
        }
    }
    
    public subscript(value: PartialRangeThrough<Int>) -> Substring {
        get {
            return self[...index(startIndex, offsetBy: value.upperBound)]
        }
    }
    
    public subscript(value: PartialRangeFrom<Int>) -> Substring {
        get {
            return self[index(startIndex, offsetBy: value.lowerBound)...]
        }
    }
}

let data = "This is a string!"

data[..<4]  // "This"
data[5..<9] // "is a"
data[10...] // "string!"

Concise syntax for sorting using a KeyPath

By using a KeyPath along with a generic type, a very clean and concise syntax for sorting data can be implemented:

import Foundation

extension Sequence {
    func sorted<T: Comparable>(by attribute: KeyPath<Element, T>) -> [Element] {
        return sorted(by: { $0[keyPath: attribute] < $1[keyPath: attribute] })
    }
}

let data = ["Some", "words", "of", "different", "lengths"]

data.sorted(by: \.count) // ["of", "Some", "words", "lengths", "different"]

If you like this syntax, make sure to checkout KeyPathKit!

Manufacturing cache-efficient versions of pure functions

By capturing a local variable in a returned closure, it is possible to manufacture cache-efficient versions of pure functions. Be careful though, this trick only works with non-recursive function!

import Foundation

func cached<In: Hashable, Out>(_ f: @escaping (In) -> Out) -> (In) -> Out {
    var cache = [In: Out]()
    
    return { (input: In) -> Out in
        if let cachedValue = cache[input] {
            return cachedValue
        } else {
            let result = f(input)
            cache[input] = result
            return result
        }
    }
}

let cachedCos = cached { (x: Double) in cos(x) }

cachedCos(.pi * 2) // value of cos for 2π is now cached

Simplifying complex conditions with pattern matching

When distinguishing between complex boolean conditions, using a switch statement along with pattern matching can be more readable than the classic series of if {} else if {}.

import Foundation

let expr1: Bool
let expr2: Bool
let expr3: Bool

if expr1 && !expr3 {
    functionA()
} else if !expr2 && expr3 {
    functionB()
} else if expr1 && !expr2 && expr3 {
    functionC()
}

switch (expr1, expr2, expr3) {
    
case (true, _, false):
    functionA()
case (_, false, true):
    functionB()
case (true, false, true):
    functionC()
default:
    break
}

Easily generating arrays of data

Using map() on a range makes it easy to generate an array of data.

import Foundation

func randomInt() -> Int { return Int(arc4random()) }

let randomArray = (1...10).map { _ in randomInt() }

Using @autoclosure for cleaner call sites

Using @autoclosure enables the compiler to automatically wrap an argument within a closure, thus allowing for a very clean syntax at call sites.

import UIKit

extension UIView {
    class func animate(withDuration duration: TimeInterval, _ animations: @escaping @autoclosure () -> Void) {
        UIView.animate(withDuration: duration, animations: animations)
    }
}

let view = UIView()

UIView.animate(withDuration: 0.3, view.backgroundColor = .orange)

Observing new and old value with RxSwift

When working with RxSwift, it's very easy to observe both the current and previous value of an observable sequence by simply introducing a shift using skip().

import RxSwift

let values = Observable.of(4, 8, 15, 16, 23, 42)

let newAndOld = Observable.zip(values, values.skip(1)) { (previous: $0, current: $1) }
    .subscribe(onNext: { pair in
        print("current: \(pair.current) - previous: \(pair.previous)")
    })

//current: 8 - previous: 4
//current: 15 - previous: 8
//current: 16 - previous: 15
//current: 23 - previous: 16
//current: 42 - previous: 23

Implicit initialization from literal values

Using protocols such as ExpressibleByStringLiteral it is possible to provide an init that will be automatically when a literal value is provided, allowing for nice and short syntax. This can be very helpful when writing mock or test data.

import Foundation

extension URL: ExpressibleByStringLiteral {
    public init(stringLiteral value: String) {
        self.init(string: value)!
    }
}

let url: URL = "http://www.google.fr"

NSURLConnection.canHandle(URLRequest(url: "http://www.google.fr"))

Achieving systematic validation of data

Through some clever use of Swift private visibility it is possible to define a container that holds any untrusted value (such as a user input) from which the only way to retrieve the value is by making it successfully pass a validation test.

import Foundation

struct Untrusted<T> {
    private(set) var value: T
}

protocol Validator {
    associatedtype T
    static func validation(value: T) -> Bool
}

extension Validator {
    static func validate(untrusted: Untrusted<T>) -> T? {
        if self.validation(value: untrusted.value) {
            return untrusted.value
        } else {
            return nil
        }
    }
}

struct FrenchPhoneNumberValidator: Validator {
    static func validation(value: String) -> Bool {
       return (value.count) == 10 && CharacterSet(charactersIn: value).isSubset(of: CharacterSet.decimalDigits)
    }
}

let validInput = Untrusted(value: "0122334455")
let invalidInput = Untrusted(value: "0123")

FrenchPhoneNumberValidator.validate(untrusted: validInput) // returns "0122334455"
FrenchPhoneNumberValidator.validate(untrusted: invalidInput) // returns nil

Implementing the builder pattern with keypaths

With the addition of keypaths in Swift 4, it is now possible to easily implement the builder pattern, that allows the developer to clearly separate the code that initializes a value from the code that uses it, without the burden of defining a factory method.

import UIKit

protocol With {}

extension With where Self: AnyObject {
    @discardableResult
    func with<T>(_ property: ReferenceWritableKeyPath<Self, T>, setTo value: T) -> Self {
        self[keyPath: property] = value
        return self
    }
}

extension UIView: With {}

let view = UIView()

let label = UILabel()
    .with(\.textColor, setTo: .red)
    .with(\.text, setTo: "Foo")
    .with(\.textAlignment, setTo: .right)
    .with(\.layer.cornerRadius, setTo: 5)

view.addSubview(label)

🚨 The Swift compiler does not perform OS availability checks on properties referenced by keypaths. Any attempt to use a KeyPath for an unavailable property will result in a runtime crash.

I share the credit for this tip with Marion Curtil.

Storing functions rather than values

When a type stores values for the sole purpose of parametrizing its functions, it’s then possible to not store the values but directly the function, with no discernable difference at the call site.

import Foundation

struct MaxValidator {
    let max: Int
    let strictComparison: Bool
    
    func isValid(_ value: Int) -> Bool {
        return self.strictComparison ? value < self.max : value <= self.max
    }
}

struct MaxValidator2 {
    var isValid: (_ value: Int) -> Bool
    
    init(max: Int, strictComparison: Bool) {
        self.isValid = strictComparison ? { $0 < max } : { $0 <= max }
    }
}

MaxValidator(max: 5, strictComparison: true).isValid(5) // false
MaxValidator2(max: 5, strictComparison: false).isValid(5) // true

Defining operators on function types

Functions are first-class citizen types in Swift, so it is perfectly legal to define operators for them.

import Foundation

let firstRange = { (0...3).contains($0) }
let secondRange = { (5...6).contains($0) }

func ||(_ lhs: @escaping (Int) -> Bool, _ rhs: @escaping (Int) -> Bool) -> (Int) -> Bool {
    return { value in
        return lhs(value) || rhs(value)
    }
}

(firstRange || secondRange)(2) // true
(firstRange || secondRange)(4) // false
(firstRange || secondRange)(6) // true

Typealiases for functions

Typealiases are great to express function signatures in a more comprehensive manner, which then enables us to easily define functions that operate on them, resulting in a nice way to write and use some powerful API.

import Foundation

typealias RangeSet = (Int) -> Bool

func union(_ left: @escaping RangeSet, _ right: @escaping RangeSet) -> RangeSet {
    return { left($0) || right($0) }
}

let firstRange = { (0...3).contains($0) }
let secondRange = { (5...6).contains($0) }

let unionRange = union(firstRange, secondRange)

unionRange(2) // true
unionRange(4) // false

Encapsulating state within a function

By returning a closure that captures a local variable, it's possible to encapsulate a mutable state within a function.

import Foundation

func counterFactory() -> () -> Int {
    var counter = 0
    
    return {
        counter += 1
        return counter
    }
}

let counter = counterFactory()

counter() // returns 1
counter() // returns 2

Generating all cases for an Enum

⚠️ Since Swift 4.2, allCases can now be synthesized at compile-time by simply conforming to the protocol CaseIterable. The implementation below should no longer be used in production code.

Through some clever leveraging of how enums are stored in memory, it is possible to generate an array that contains all the possible cases of an enum. This can prove particularly useful when writing unit tests that consume random data.

import Foundation

enum MyEnum { case first; case second; case third; case fourth }

protocol EnumCollection: Hashable {
    static var allCases: [Self] { get }
}

extension EnumCollection {
    public static var allCases: [Self] {
        var i = 0
        return Array(AnyIterator {
            let next = withUnsafePointer(to: &i) {
                $0.withMemoryRebound(to: Self.self, capacity: 1) { $0.pointee }
            }
            if next.hashValue != i { return nil }
            i += 1
            return next
        })
    }
}

extension MyEnum: EnumCollection { }

MyEnum.allCases // [.first, .second, .third, .fourth]

Using map on optional values

The if-let syntax is a great way to deal with optional values in a safe manner, but at times it can prove to be just a little bit to cumbersome. In such cases, using the Optional.map() function is a nice way to achieve a shorter code while retaining safeness and readability.

import UIKit

let date: Date? = Date() // or could be nil, doesn't matter
let formatter = DateFormatter()
let label = UILabel()

if let safeDate = date {
    label.text = formatter.string(from: safeDate)
}

label.text = date.map { return formatter.string(from: $0) }

label.text = date.map(formatter.string(from:)) // even shorter, tough less readable

📣 NEW 📣 Swift Tips are now available on YouTube 👇

Summary

#57 Property Wrappers as Debugging Tools
#56 Localization through String interpolation
#55 Implementing pseudo-inheritance between structs
#54 Composing NSAttributedString through a Function Builder
#53 Using switch and if as expressions
#52 Avoiding double negatives within guard statements
#51 Defining a custom init without loosing the compiler-generated one
#50 Implementing a namespace through an empty enum
#49 Using Never to represent impossible code paths
#48 Providing a default value to a Decodable enum
#47 Another lightweight dependency injection through default values for function parameters
#46 Lightweight dependency injection through protocol-oriented programming
#45 Getting rid of overabundant [weak self] and guard
#44 Solving callback hell with function composition
#43 Transform an asynchronous function into a synchronous one
#42 Using KeyPaths instead of closures
#41 Bringing some type-safety to a userInfo Dictionary
#40 Lightweight data-binding for an MVVM implementation
#39 Using typealias to its fullest
#38 Writing an interruptible overload of forEach
#37 Optimizing the use of reduce()
#36 Avoiding hardcoded reuse identifiers
#35 Defining a union type
#34 Asserting that classes have associated NIBs and vice-versa
#33 Small footprint type-erasing with functions
#32 Performing animations sequentially
#31 Debouncing a function call
#30 Providing useful operators for Optional booleans
#29 Removing duplicate values from a Sequence
#28 Shorter syntax to deal with optional strings
#27 Encapsulating background computation and UI update
#26 Retrieving all the necessary data to build a debug view
#25 Defining a function to map over dictionaries
#24 A shorter syntax to remove nil values
#23 Dealing with expirable values
#22 Using parallelism to speed-up map()
#21 Measuring execution time with minimum boilerplate
#20 Running two pieces of code in parallel
#19 Making good use of #file, #line and #function
#18 Comparing Optionals through Conditional Conformance
#17 Safely subscripting a Collection
#16 Easier String slicing using ranges
#15 Concise syntax for sorting using a KeyPath
#14 Manufacturing cache-efficient versions of pure functions
#13 Simplifying complex condition with pattern matching
#12 Easily generating arrays of data
#11 Using @autoclosure for cleaner call sites
#10 Observing new and old value with RxSwift
#09 Implicit initialization from literal values
#08 Achieving systematic validation of data
#07 Implementing the builder pattern with keypaths
#06 Storing functions rather than values
#05 Defining operators on function types
#04 Typealiases for functions
#03 Encapsulating state within a function
#02 Generating all cases for an Enum
#01 Using map on optional values

Tips

Download Details:

Author: vincent-pradeilles
Source code: https://github.com/vincent-pradeilles/swift-tips

License: MIT license
#swift

Colin Padayachee

1625198214

Using the Linux Command Line to Convert PDF to Image

To use the pdftoppm command-line tool, you need to first install pdftoppm which is a part of the poppler / poppler-utils / poppler-tools package. Install this package as follows depending on your Linux distribution

1. Convert PDF Document to Image

2. Convert Range of PDF Pages to Images

3. Convert First PDF Page to Image

4. Adjust DPI Quality to Conversion

#convert pdf #linux command line #linux #command line

Dejah Reinger

1599859380

How to Do API Testing?

Nowadays API testing is an integral part of testing. There are a lot of tools like postman, insomnia, etc. There are many articles that ask what is API, What is API testing, but the problem is How to do API testing? What I need to validate.

Note: In this article, I am going to use postman assertions for all the examples since it is the most popular tool. But this article is not intended only for the postman tool.

Let’s directly jump to the topic.

Let’s consider you have an API endpoint example http://dzone.com/getuserDetails/{{username}} when you send the get request to that URL it returns the JSON response.

My API endpoint is http://dzone.com/getuserDetails/{{username}}

The response is in JSON format like below

JSON

{
  "jobTitle": "string",
  "userid": "string",
  "phoneNumber": "string",
  "password": "string",
  "email": "user@example.com",
  "firstName": "string",
  "lastName": "string",
  "userName": "string",
  "country": "string",
  "region": "string",
  "city": "string",
  "department": "string",
  "userType": 0
}

In the JSON we can see there are properties and associated values.

Now, For example, if we need details of the user with the username ‘ganeshhegde’ we need to send a **GET **request to **http://dzone.com/getuserDetails/ganeshhegde **

dzone.com

Now there are two scenarios.

1. Valid Usecase: User is available in the database and it returns user details with status code 200

2. Invalid Usecase: User is Unavailable/Invalid user in this case it returns status with code 404 with not found message.

#tutorial #performance #api #test automation #api testing #testing and qa #application programming interface #testing as a service #testing tutorial #api test

Colin Padayachee

1625631509

Examples of the dig command in Linux

Dig Command Line Options and Examples
Here is the frequently used command line options and example’s of dig command.
1. Basic Dig Command
A basic dig command accept domain name as command line parameter and prints Address record.
2. Query With Specific DNS Server
The default dig command queries to dns server configured on your system. For example, the Linux systems keep default DNS entry in /etc/resolv.conf.
3. Print Short Answer
Use +short command line option to print result in short form. This is basically useful with the shell scripting and other automation tasks.
4. Print Detailed but Specific Result
Use +noall with +answer to print detailed information but specific. This will print only answer section including few more details as a result.

#linux commands #command #dig #dig command #useful examples #linux

Commander: Test Your Command Line interfaces on Windows, Linux and Osx

Installation

Any system with Go installed

Linux & osx

Windows

Quick start

Complete YAML file

Executing

Adding tests

Documentation

Usage

Tests

command

config

exit-code

stdout

stderr

skip

Config

dir

env

inherit-env

interval

retries

timeout

Nodes

local

ssh

docker

Development

Misc

What is GEEK

Buddha Community

Commander: Test Your Command Line interfaces on Windows, Linux and Osx

Installation

Any system with Go installed

Linux & osx

Windows

Quick start

Complete YAML file

Executing

Adding tests

Documentation

Usage

Tests

command

config

exit-code

stdout

stderr

skip

Config

dir

env

inherit-env

interval

retries

timeout

Nodes

local

ssh

docker

Development

Misc

Swift Tips: A Collection Useful Tips for The Swift Language

SwiftTips

Property Wrappers as Debugging Tools

Localization through String interpolation

Implementing pseudo-inheritance between structs

Composing NSAttributedString through a Function Builder

Using switch and if as expressions

Avoiding double negatives within guard statements

Defining a custom init without loosing the compiler-generated one

Implementing a namespace through an empty enum

Using Never to represent impossible code paths

Providing a default value to a Decodable enum

Another lightweight dependency injection through default values for function parameters

Lightweight dependency injection through protocol-oriented programming

Getting rid of overabundant [weak self] and guard

Solving callback hell with function composition

Localization through `String` interpolation

Implementing pseudo-inheritance between `structs`

Composing `NSAttributedString` through a Function Builder

Using `switch` and `if` as expressions

Avoiding double negatives within `guard` statements

Defining a custom `init` without loosing the compiler-generated one

Implementing a namespace through an empty `enum`

Using `Never` to represent impossible code paths

Providing a default value to a `Decodable` `enum`

Getting rid of overabundant `[weak self]` and `guard`

Bringing some type-safety to a `userInfo` `Dictionary`

Using `typealias` to its fullest

Writing an interruptible overload of `forEach`

Optimizing the use of `reduce()`

Providing useful operators for `Optional` booleans

Removing duplicate values from a `Sequence`

A shorter syntax to remove `nil` values

Using parallelism to speed-up `map()`