expect-more-jest

expect-more-jest

Write Beautiful Specs with Custom Matchers for Jest

Table of Contents

• Overview
• 🌩 Installation
• 🕹 Configuration
• 🧪 Generators
• 🔬 Matchers
• 🙋🏽‍♂️ Getting Help
• 👀 Other Projects
• 🤓 Author

Overview

expect-more-jest is a huge library of test matchers for a range of common use-cases, to make tests easier to read and produce relevant and useful messages when they fail.

Avoid vague messages such as "expected false to be true" in favour of useful cues like "expected 3 to be even number", and avoid implementation noise such as expect(paws.length % 2 === 0).toEqual(true) in favour of simply stating that you expect(paws.length).toBeEvenNumber().

🌩 Installation

npm install expect-more-jest --save-dev

🕹 Configuration

The simplest way to integrate is to set the setupFilesAfterEnv array of Jest's jest.config.js to include require.resolve('expect-more-jest').

Note: If your Editor does not recognise that you are using custom matchers, add a global.d.ts file at the root of your project containing:

import 'expect-more-jest';

🧪 Generators

expect-more/gen helps you assert how your application under test behaves when parts of its input data are missing or null.

import { withMissingNodes } from 'expect-more/gen';

it('should return null if any part of the API contract is broken', () => {
  for (let brokenContract of withMissingNodes(contract)) {
    expect(fn(brokenContract)).toBeNull();
  }
});

🔬 Matchers

expect(new Date('2020-01-01')).toBeAfter(new Date('2019-12-31'));
expect([true, false, new Boolean(true)]).toBeArrayOfBooleans();
expect([12, 0, 14]).toBeArrayOfNumbers();
expect([{}, new Object()]).toBeArrayOfObjects();
expect(['i', 'contain', 4, 'items']).toBeArrayOfSize(4);
expect(['we', 'are', 'all', 'strings']).toBeArrayOfStrings();
expect([2, true, 'string']).toBeArray();
expect(async () => {
  await fetch('...');
}).toBeAsyncFunction();
expect(new Date('2019-12-31')).toBeBefore(new Date('2020-01-01'));
expect(false).toBeBoolean();
expect('100').toBeCalculable();
expect(new Date('2019-12-31')).toBeDate();
expect(12.55).toBeDecimalNumber();
expect(12).toBeDivisibleBy(2);
expect([]).toBeEmptyArray();
expect({}).toBeEmptyObject();
expect('').toBeEmptyString();
expect(2).toBeEvenNumber();
expect(false).toBeFalse();
expect(() => 'i am a function').toBeFunction();
expect(function* gen() {
  yield 'i am a generator';
}).toBeGeneratorFunction();
expect('1999-12-31T23:59:59').toBeIso8601();
expect('{"i":"am valid JSON"}').toBeJsonString();
expect(['i', 'have', 3]).toBeLongerThan([2, 'items']);
expect(['i', 'am not empty']).toBeNonEmptyArray();
expect({ i: 'am not empty' }).toBeNonEmptyObject();
expect('i am not empty').toBeNonEmptyString();
expect(8).toBeNumber();
expect({}).toBeObject();
expect(5).toBeOddNumber();
expect(new RegExp('i am a regular expression')).toBeRegExp();
expect(['i also have', '2 items']).toBeSameLengthAs(['i have', '2 items']);
expect(['i have one item']).toBeShorterThan(['i', 'have', 4, 'items']);
expect('i am a string').toBeString();
expect(true).toBeTrue();
expect(new Date('2020-01-01')).toBeValidDate();
expect({}).toBeWalkable();
expect(' ').toBeWhitespace();
expect(8).toBeWholeNumber();
expect(7).toBeWithinRange(0, 10);
expect('JavaScript').toEndWith('Script');
expect({ child: { grandchild: [true, false, new Boolean(true)] } }).toHaveArrayOfBooleans(
  'child.grandchild',
);
expect({ child: { grandchild: [12, 0, 14] } }).toHaveArrayOfNumbers('child.grandchild');
expect({ child: { grandchild: [{}, new Object()] } }).toHaveArrayOfObjects('child.grandchild');
expect({ child: { grandchild: ['i', 'contain', 4, 'items'] } }).toHaveArrayOfSize(
  'child.grandchild',
  4,
);
expect({ child: { grandchild: ['we', 'are', 'all', 'strings'] } }).toHaveArrayOfStrings(
  'child.grandchild',
);
expect({ child: { grandchild: [2, true, 'string'] } }).toHaveArray('child.grandchild');
expect({
  child: {
    grandchild: async () => {
      await fetch('...');
    },
  },
}).toHaveAsyncFunction('child.grandchild');
expect({ child: { grandchild: false } }).toHaveBoolean('child.grandchild');
expect({ child: { grandchild: '100' } }).toHaveCalculable('child.grandchild');
expect({ child: { grandchild: new Date('2020-01-01') } }).toHaveDateAfter(
  'child.grandchild',
  new Date('2019-12-31'),
);
expect({ child: { grandchild: new Date('2019-12-31') } }).toHaveDateBefore(
  'child.grandchild',
  new Date('2020-01-01'),
);
expect({ child: { grandchild: new Date('2019-12-31') } }).toHaveDate('child.grandchild');
expect({ child: { grandchild: 12.55 } }).toHaveDecimalNumber('child.grandchild');
expect({ child: { grandchild: 12 } }).toHaveDivisibleBy('child.grandchild', 2);
expect({ child: { grandchild: [] } }).toHaveEmptyArray('child.grandchild');
expect({ child: { grandchild: {} } }).toHaveEmptyObject('child.grandchild');
expect({ child: { grandchild: '' } }).toHaveEmptyString('child.grandchild');
expect({ child: { grandchild: 'JavaScript' } }).toHaveEndingWith('child.grandchild', 'Script');
expect({ child: { grandchild: 2 } }).toHaveEvenNumber('child.grandchild');
expect({ child: { grandchild: false } }).toHaveFalse('child.grandchild');
expect({
  child: {
    grandchild: function* gen() {
      yield 'i am a generator';
    },
  },
}).toHaveGeneratorFunction('child.grandchild');
expect({ child: { grandchild: 10 } }).toHaveGreaterThanOrEqualTo('child.grandchild', 5);
expect({ child: { grandchild: '1999-12-31T23:59:59' } }).toHaveIso8601('child.grandchild');
expect({ child: { grandchild: '{"i":"am valid JSON"}' } }).toHaveJsonString('child.grandchild');
expect({ child: { grandchild: 8 } }).toHaveLessThanOrEqualTo('child.grandchild', 12);
expect({ child: { grandchild: ['i', 'have', 3] } }).toHaveLongerThan('child.grandchild', [
  2,
  'items',
]);
expect({ child: { grandchild: () => 'i am a function' } }).toHaveMethod('child.grandchild');
expect({ child: { grandchild: ['i', 'am not empty'] } }).toHaveNonEmptyArray('child.grandchild');
expect({ child: { grandchild: { i: 'am not empty' } } }).toHaveNonEmptyObject('child.grandchild');
expect({ child: { grandchild: 'i am not empty' } }).toHaveNonEmptyString('child.grandchild');
expect({ child: { grandchild: null } }).toHaveNull('child.grandchild');
expect({ child: { grandchild: 4.8 } }).toHaveNumberNear('child.grandchild', 5, 0.5);
expect({ child: { grandchild: 7 } }).toHaveNumberWithinRange('child.grandchild', 0, 10);
expect({ child: { grandchild: 8 } }).toHaveNumber('child.grandchild');
expect({ child: { grandchild: {} } }).toHaveObject('child.grandchild');
expect({ child: { grandchild: 5 } }).toHaveOddNumber('child.grandchild');
expect({ child: { grandchild: new RegExp('i am a regular expression') } }).toHaveRegExp(
  'child.grandchild',
);
expect({ child: { grandchild: ['i also have', '2 items'] } }).toHaveSameLengthAs(
  'child.grandchild',
  ['i have', '2 items'],
);
expect({ child: { grandchild: ['i have one item'] } }).toHaveShorterThan('child.grandchild', [
  'i',
  'have',
  4,
  'items',
]);
expect({ child: { grandchild: 'JavaScript' } }).toHaveStartingWith('child.grandchild', 'Java');
expect({ child: { grandchild: 'i am a string' } }).toHaveString('child.grandchild');
expect({ child: { grandchild: true } }).toHaveTrue('child.grandchild');
expect({ child: { grandchild: undefined } }).toHaveUndefined('child.grandchild');
expect({ child: { grandchild: new Date('2020-01-01') } }).toHaveValidDate('child.grandchild');
expect({ child: { grandchild: {} } }).toHaveWalkable('child.grandchild');
expect({ child: { grandchild: ' ' } }).toHaveWhitespace('child.grandchild');
expect({ child: { grandchild: 8 } }).toHaveWholeNumber('child.grandchild');
expect('JavaScript').toStartWith('Java');

🙋🏽‍♂️ Getting Help

Get help with issues by creating a Bug Report or discuss ideas by opening a Feature Request.

👀 Other Projects

If you find my Open Source projects useful, please share them ❤️

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🤓 Author

I'm Jamie Mason from Leeds in England, I began Web Design and Development in 1999 and have been Contracting and offering Consultancy as Fold Left Ltd since 2012. Who I've worked with includes Sky Sports, Sky Bet, Sky Poker, The Premier League, William Hill, Shell, Betfair, and Football Clubs including Leeds United, Spurs, West Ham, Arsenal, and more.