expect-matchers

Why

TL;DR

Until and if jest-community/jest-extended#640 is merged I need better toIncludeSameMembers

Currently, if you have a test like this and is using jest-extended:

it('example', () => {
	const expected = Array.from({ length: 1000 }, (_, i) => ({
		i,
		value: 'expected'
	}));
	const actual = [...expected];
	const tmp = actual[200];
	actual[200] = actual[201];
	actual[201] = { ...tmp, value: 'hope you find me' };

	expect(actual).toIncludeSameMembers(expected);
});

You will get an error like this:

   expect(received).toIncludeSameMembers(expected)

    Expected list to have the following members and no more:
      [{"i": 0, "value": "expected"}, {"i": 1, "value": "expected"}, {"i": 2, "value": "expected"}, {"i": 3, "value": "expected"}, {"i": 4, "value": "expected"}, {"i": 5, "value": "expected"}, {"i": 6, "value": "expected"}, {"i": 7, "value": "expected"}, {"i": 8, "value": "expected"}, {"i": 9, "value": "expected"}, …]
    Received:
      [{"i": 0, "value": "expected"}, {"i": 1, "value": "expected"}, {"i": 2, "value": "expected"}, {"i": 3, "value": "expected"}, {"i": 4, "value": "expected"}, {"i": 5, "value": "expected"}, {"i": 6, "value": "expected"}, {"i": 7, "value": "expected"}, {"i": 8, "value": "expected"}, {"i": 9, "value": "expected"}, …]

      410 |             actual[201] = { ...tmp, value: 'hope you find me' };
      411 |
    > 412 |             expect(actual).toIncludeSameMembers(expected);
          |                            ^
      413 |     });

which is very hard to understand so I instead this will be the error message:

    expect(received).toIncludeSameMembers(expected)

    - Expected  - 1
    + Received  + 1

    @@ -799,11 +799,11 @@
          "i": 199,
          "value": "expected",
        },
        Object {
          "i": 200,
    -     "value": "expected",
    +     "value": "hope you find me",
        },
        Object {
          "i": 201,
          "value": "expected",
        },

      410 |             actual[201] = { ...tmp, value: 'hope you find me' };
      411 |
    > 412 |             expect(actual).toIncludeSameMembers(expected);
          |                            ^
      413 |     });

Installation

With npm:

npm install --save-dev expect-matchers

With yarn:

yarn add -D expect-matchers

Setup

// ./testSetup.js

// add all expect-matchers matchers
import * as matchers from 'expect-matchers';
expect.extend(matchers);

// or just add specific matchers
import { toIncludeSameMembers } from 'expect-matchers';
expect.extend({ sinonToBeCalled, sinonToBeCalledTimes });

Add your setup script at the beginning of each test in jest it called (setupFilesAfterEnv)

If you use jest

Add your setup script to your Jest setupFilesAfterEnv configuration. See for help

"jest": {
  "setupFilesAfterEnv": ["./testSetup.js"]
}

To automatically extend expect with all matchers, you can use

"jest": {
  "setupFilesAfterEnv": ["expect-matchers/all"]
}

Typescript

If your editor does not recognise the custom expect-matchers matchers, add a global.d.ts file to your project with:

import 'expect-matchers';

If you also use jest-extended

If you also use jest-extended you should not extend expect with the matcher toIncludeSameMembers as it can cause undefined behavior

Matchers

.toIncludeSameMembers([members, fnOrKey?])

test('passes when arrays match in a different order', () => {
  expect([1, 2, 3]).toIncludeSameMembers([3, 1, 2]);
  expect([{ foo: 'bar' }, { baz: 'qux' }]).toIncludeSameMembers([{ baz: 'qux' }, { foo: 'bar' }]);
});

If you are working with objects

For best error output you should pass a key or a function that will return a unique key to the matcher so we can display the error better

test('passes when arrays match in a different order', () => {
  expect([{ id: 2, foo: 'bar' }, { id: 1, baz: 'qux' }]).toIncludeSameMembers([{ id: 1, baz: 'QUX' }, { id: 2, foo: 'bar' }], 'id');
  expect([{ id: 2, foo: 'bar' }, { id: 1, baz: 'qux' }]).toIncludeSameMembers([{ id: 1, baz: 'QUX' }, { id: 2, foo: 'bar' }], (itemA, itemB) => itemA.id === itemB.id);
});

Inspirations and credits

jest-extended for the loading, setup some of the code and the file directory structure