https://github.com/testdouble/testdouble-jest

A testdouble.js extension to add support for Jest module mocking
https://github.com/testdouble/testdouble-jest

Last synced: 7 days ago
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A testdouble.js extension to add support for Jest module mocking

• Host: GitHub
• URL: https://github.com/testdouble/testdouble-jest
• Owner: testdouble
• License: mit
• Created: 2018-02-10T22:06:38.000Z (over 6 years ago)
• Default Branch: main
• Last Pushed: 2021-06-02T08:57:04.000Z (over 3 years ago)
• Last Synced: 2024-10-25T02:43:55.360Z (14 days ago)
• Language: JavaScript
• Size: 55.7 KB
• Stars: 37
• Watchers: 5
• Forks: 5
• Open Issues: 3
• Metadata Files:
  • Readme: README.md
  • License: LICENSE.txt

Awesome Lists containing this project

• awesome-jest - testdouble-jest

README

        
# testdouble-jest

Support for [testdouble.js](https://github.com/testdouble/testdouble.js) for

users of [Jest](https://github.com/facebook/jest)!

Note that testdouble-jest requires [email protected] and [email protected] or higher to work.

## Installation

```

$ npm i -D testdouble-jest

```

Then, from a test helper (we recommend setting a

[setupFilesAfterEnv](https://jestjs.io/docs/en/configuration.html#setupfilesafterenv-array)

module), invoke the module and pass in both `td` and `jest`, like so:

```js

global.td = require('testdouble')

require('testdouble-jest')(td, jest)

```

For an example of a helper that sets up testdouble.js, testdouble-jest, and

ensures `td.reset()` is called after each test, look at

[example/helper.js](/example/helper.js) in this repo.

## Usage

When you invoke `testdouble-jest`, it does two things: (1) adds support for

using `td.replace()` for module replacement in Jest tests, and (2) adds a new

top-level `td.mock()` function that mirrors the `jest.mock()` API.

We recommend using `td.replace()`, since it's terser (by returning the fake

instead of the `jest` object) and your use of testdouble.js will remain portable

even if you were to move to a different test runner.

**`td.replace(moduleName[, manualStub])`**

Once you've initialized testdouble-jest in your test run, `td.replace()` will be

able to replace modules just as it does in any other test runner (as of 

[email protected]). Functionally, it's delegates to `td.mock()`, but behaves just 

as it [always

has](https://github.com/testdouble/testdouble.js#module-replacement-with-nodejs)

for module replacement.

Here's a trivial example:

```js

let loadInvoices, subject

describe('td.replace', () => {

  beforeEach(() => {

    loadInvoices = td.replace('./load-invoices')

    subject = require('./calculate-payment')

  })

  it('calculates payments', () => {

    td.when(loadInvoices(2018, 7)).thenReturn([24,28])

    const result = subject('2018-07')

    expect(result).toEqual(52)

  })

})

```

For a runnable example, check

[example/td-replace.test.js](/example/td-replace.test.js).

**`td.mock(moduleName[, moduleFactory, options])`**

`td.mock()` is designed to have the same API as

[`jest.mock()`](https://facebook.github.io/jest/docs/en/es6-class-mocks.html).

If you just pass a module name to `td.mock()`, it will imitate the real

dependency and use Jest's own module replacement facility to ensure that any

`require()` calls by your test subject receive the testdouble fake, as opposed

to the real dependency. There's an example in this repo at

[example/td-mock.test.js](/example/td-mock.test.js).

If you've used `jest.mock()` before, `td.mock()` will seem pretty familiar.

`td.mock()` returns the `jest` object (since that's what

`jest.mock()` does), so your test will also need to `require()` the thing you

just faked if you want to set up any stubbings or invocation assertions.

Note that if you provide a `moduleFactory` and/or `options` argument, `td.mock`

will simply delegate to `jest.mock`, since it won't have anything

testdouble.js-specific to do.