valid-expect.md

Enforce valid expect() usage (valid-expect)

Ensure expect() is called with a single argument and there is an actual expectation made.

Rule details

This rule triggers a warning if expect() is called with more than one argument or without arguments. It would also issue a warning if there is nothing called on expect(), e.g.:

expect();
expect('something');

or when a matcher function was not called, e.g.:

expect(true).toBeDefined;

or when an async assertion was not awaited or returned, e.g.:

expect(Promise.resolve('Hi!')).resolves.toBe('Hi!');

This rule is enabled by default.

Options

{
  type: 'object',
  properties: {
    alwaysAwait: {
      type: 'boolean',
      default: false,
    },
    asyncMatchers: {
      type: 'array',
      items: { type: 'string' },
      default: ['toResolve', 'toReject'],
    },
    minArgs: {
      type: 'number',
      minimum: 1,
    },
    maxArgs: {
      type: 'number',
      minimum: 1,
    },
  },
  additionalProperties: false,
}

alwaysAwait

Enforces to use await inside block statements. Using return will trigger a warning. Returning one line statements with arrow functions is always allowed.

Examples of incorrect code for the { "alwaysAwait": true } option:

// alwaysAwait: true
test('test1', async () => {
  await expect(Promise.resolve(2)).resolves.toBeDefined();
  return expect(Promise.resolve(1)).resolves.toBe(1); // `return` statement will trigger a warning
});

Examples of correct code for the { "alwaysAwait": true } option:

// alwaysAwait: true
test('test1', async () => {
  await expect(Promise.resolve(2)).resolves.toBeDefined();
  await expect(Promise.resolve(1)).resolves.toBe(1);
});

test('test2', () => expect(Promise.resolve(2)).resolves.toBe(2));

asyncMatchers

Allows specifying which matchers return promises, and so should be considered async when checking if an expect should be returned or awaited.

By default, this has a list of all the async matchers provided by jest-extended (namely, toResolve and toReject).

minArgs & maxArgs

Enforces the minimum and maximum number of arguments that expect can take, and is required to take.

Both of these properties have a default value of 1, which is the number of arguments supported by vanilla expect.

This is useful when you're using libraries that increase the number of arguments supported by expect, such as jest-expect-message.

Default configuration

The following patterns are considered warnings:

test('all the things', async () => {
  expect();
  expect().toEqual('something');
  expect('something', 'else');
  expect('something');
  await expect('something');
  expect(true).toBeDefined;
  expect(Promise.resolve('hello')).resolves;
  expect(Promise.resolve('hello')).resolves.toEqual('hello');
  Promise.resolve(expect(Promise.resolve('hello')).resolves.toEqual('hello'));
  Promise.all([
    expect(Promise.resolve('hello')).resolves.toEqual('hello'),
    expect(Promise.resolve('hi')).resolves.toEqual('hi'),
  ]);
});

The following patterns are not warnings:

test('all the things', async () => {
  expect('something').toEqual('something');
  expect([1, 2, 3]).toEqual([1, 2, 3]);
  expect(true).toBeDefined();
  await expect(Promise.resolve('hello')).resolves.toEqual('hello');
  await Promise.resolve(
    expect(Promise.resolve('hello')).resolves.toEqual('hello'),
  );
  await Promise.all([
    expect(Promise.resolve('hello')).resolves.toEqual('hello'),
    expect(Promise.resolve('hi')).resolves.toEqual('hi'),
  ]);
});