JavaScript Unit Test Best Practices

JavaScript Unit Test Best Practices

Dividing our tests for more complete coverage. 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.

Don’t Test Multiple Concerns in the Same Test

We should only test one thing in each test to keep things simple.

It’ll help us locate any problems easier if we find issues.

For example, instead of writing:

it('should save profile data and update the view with profile data', () => {
  // expect(...)to(...);
  // expect(...)to(...);
});

We write:

it('should save profile data', () => {
  // expect(...)to(...);
});
it('should update the view with profile data', () => {
  // expect(...)to(...);
});

Writing ‘and’ or ‘or’ in the test description means that we should break them up into multiple tests.

Cover the General Case and the Edge Cases

We got to cover edge cases so that we won’t miss anything.

They’re easy to miss but people will notice them.

For instance, instead of writing:”

it('should properly calculate arithmetic expression', () => {
  const result = calculate('(5 + 10) / 2');
  expect(result).toBe(7.5);
});

We write:

describe('The arithmetic expression calculator', () => {
  it('should return null when the expression is an empty string', () => {
    const result = calculator('');
    expect(result).toBeNull();
  });
  it('should return value if expression is the value', () => {
    const result = calculator('12');
    expect(result).toBe(12);
  });
  it('should properly calculate arithmetic expression', () => {
    const result = calculate('(5 + 10) / 2');
    expect(result).toBe(7.5);
  });
  it('should throw an error whenever an invalid expression is passed', () => {
    const calc = () => calculator('1 + 1 -');
    expect(calc).toThrow();
  });
});

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