mattphillips/ jest-chain
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Description
Chain Jest matchers together to create one powerful assertion 🃏⛓
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jest-chain
🃏⛓
Chain Jest matchers together to create one powerful assertion
- 🍸 Less code duplication
- 🤗 Chain core and custom matchers together
- 👾 Expressive assertions
- 🚨 Fail fast assertions
Problem
Often in Jest when you are writing tests you may want to perform multiple assertions on the same variable. Currently to achieve this you have to write an individual
expectfor each assertion.
For example:
it('add 1 and 1', () => {
const actual = 1 + 1;
expect(actual).toBe(2);
expect(actual).toBeGreaterThan(1);
expect(actual).toBeLessThan(3);
});
With
jest-chainthis can instead be written by chaining the matchers together:
it('add 1 and 1', () => {
expect(1 + 1)
.toBe(2)
.toBeGreaterThan(1)
.toBeLessThan(3);
});
Installation
With npm:
npm install --save-dev jest-chain
With yarn:
yarn add -D jest-chain
Setup
Add
jest-chainto your Jest
setupFilesAfterEnvconfiguration. See for help
Jest >v24
"jest": {
"setupFilesAfterEnv": ["jest-chain"]
}
Jest <v23
"jest": {
"setupTestFrameworkScriptFile": "jest-chain"
}
If you are already using another test framework, like jest-extended, then you should create a test setup file and
requireeach of the frameworks you are using (including
jest-chain😉)
For example:
// ./testSetup.js
require('jest-chain');
require('any other test framework libraries you are using');
Then in your Jest config:
"jest": {
"setupTestFrameworkScriptFile": "./testSetup.js"
}
Typescript
If your editor does not recognise the chained jest matchers, add a
global.d.tsfile to your project with:
import 'jest-chain';
Note: if you are using any other custom matcher libraries then make sure that the
jest-chaintype import is at the bottom so that the types can chain core matchers with your customer matcher library.
Usage
Use Jest's
expectfunction the same way you would normally but with the ability to chain any matcher to another, including nested matchers such as:
.not,
.resolvesand
.rejects.
jest-chainsupports custom Jest matchers, like jest-extended, in the usual way with
expect.extend(matcher). Each of these custom matchers are also chainable.
Some examples:
expect([1, 2, 3]) .toHaveLength(3) .toEqual([1, 2, 3]);
// with jest-extended expect([1, 2, 3]) .toBeArray() .toBeArrayOfSize(3) .toEqual([1, 2, 3]) .toIncludeAnyMembers([1, 2]);expect(100) .toBePositive() .toBeGreaterThan(99) .toBeLessThan(101) .toBeNumber() .not.toBeNaN() .toBe(100);
expect('hello world') .toBeString() .toEqualCaseInsensitive('HELLO WORLD') .toStartWith('hello') .toEndWith('world') .not.toInclude('!') .toBe('hello world');
Matcher failures will fail fast from left to right, they have no impact on each other. 🎉
Note:
jest-chaindoes not currently support asymmetric matcher chaining, if you want this please send a PR 😊