no-conditional-expect.md

Prevent calling expect conditionally (no-conditional-expect)

This rule prevents the use of expect in conditional blocks, such as ifs & catchs.

This includes using expect in callbacks to functions named catch, which are assumed to be promises.

Rule Details

Jest considered a test to have failed if it throws an error, rather than on if any particular function is called, meaning conditional calls to expect could result in tests silently being skipped.

Additionally, conditionals tend to make tests more brittle and complex, as they increase the amount of mental thinking needed to understand what is actually being tested.

While expect.assertions & expect.hasAssertions can help prevent tests from silently being skipped, when combined with conditionals they typically result in even more complexity being introduced.

The following patterns are warnings:

it('foo', () => {
  doTest && expect(1).toBe(2);
});

it('bar', () => {
  if (!skipTest) {
    expect(1).toEqual(2);
  }
});

it('baz', async () => {
  try {
    await foo();
  } catch (err) {
    expect(err).toMatchObject({ code: 'MODULE_NOT_FOUND' });
  }
});

it('throws an error', async () => {
  await foo().catch(error => expect(error).toBeInstanceOf(error));
});

The following patterns are not warnings:

it('foo', () => {
  expect(!value).toBe(false);
});

function getValue() {
  if (process.env.FAIL) {
    return 1;
  }

  return 2;
}

it('foo', () => {
  expect(getValue()).toBe(2);
});

it('validates the request', () => {
  try {
    processRequest(request);
  } catch {
    // ignore errors
  } finally {
    expect(validRequest).toHaveBeenCalledWith(request);
  }
});

it('throws an error', async () => {
  await expect(foo).rejects.toThrow(Error);
});