JavaScript Unit Test Best Practices 

JavaScript Unit Test Best Practices 

Why we should focus on behavior checks? Unit tests are very useful for checking how our app is working. Otherwise, we run into all kinds of issues later on. In this article, we’ll look at some best practices we should follow when writing JavaScript unit tests.

Unit tests are very useful for checking how our app is working.

Otherwise, we run into all kinds of issues later on.

In this article, we’ll look at some best practices we should follow when writing JavaScript unit tests.

Design for Lean Testing

Test code should be simple, short, and abstraction free.

They should also be lean.

The less complexity our test code has, the better it is.

We just do something and check the results in our tests.

Include 3 Parts in Each Test Name

We should have 3 parts in each test name.

The first part is the module being tested.

The 2nd is the circumstance that we’re testing the code in.

The expected result is what we’re checking for in our test.

This way, we can tell what’s being tested and find out what to fix if it fails.

For example, we write:

describe('User Service', function() {
  describe('Add new user', function() {
    it('When no password is specified, then the product status is pending', ()=> {
      const user = new UserService().add(...);
      expect(user.status).to.equal('pending');
    });
  });
});

Structure Tests by the AAA pattern

We should structure our tests with the AAA pattern.

The 3 A’s stands for Arrange, Act, and Assert.

Arrange means the setup code is added to let us do the test.

Act is doing the test.

Assert is checking the result after doing what we have.

So if we have:

describe('User Service', function() {
  describe('login', function() {
    it('if the password is wrong, then we cannot log in', () => {
      const user = new UserService().add({ username: 'james', password: '123456' });
      const result = login('james', '123'); 
      expect(result).to.equal(false);
    });
  });
});

We arrange with the first line of the test.

Act is the call for the login function.

Assert is the expect call.

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