https://github.com/janhesters/mock-function

A simple mock function to mock functions.
https://github.com/janhesters/mock-function

jest mocking mocking-utility riteway testing testing-tool

Last synced: 4 months ago
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A simple mock function to mock functions.

• Host: GitHub
• URL: https://github.com/janhesters/mock-function
• Owner: janhesters
• License: mit
• Created: 2020-12-13T11:35:49.000Z (about 4 years ago)
• Default Branch: main
• Last Pushed: 2023-03-29T07:01:26.000Z (almost 2 years ago)
• Last Synced: 2024-09-17T02:20:43.767Z (5 months ago)
• Topics: jest, mocking, mocking-utility, riteway, testing, testing-tool
• Language: TypeScript
• Homepage:
• Size: 860 KB
• Stars: 5
• Watchers: 2
• Forks: 1
• Open Issues: 5
• Metadata Files:
  • Readme: README.md
  • Changelog: CHANGELOG.md
  • License: LICENSE

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README

        
# mock-function

A simple mock function to mock functions.

Inspired by

[`jest.fn`](https://jestjs.io/docs/en/jest-object#jestfnimplementation).

## Installation

Install the package.

```

# NPM

npm i --save-dev mock-function

# yarn

yarn add --dev mock-function

```

Import it in your tests.

```ts

import fn from 'mock-function';

```

## Usage

```ts

import mockFunction from 'mock-function';

const add = (a: number, b: number) => a + b;

const mockedAdd = mockFunction(add);

mockedAdd.hasBeenCalled();

// ↵ false

mockedAdd.hasBeenCalledWith(21, 21);

// ↵ false

mockedAdd.hasBeenCalledTimes;

// ↵ 0

mockedAdd.calls;

// ↵ []

mockedAdd(21, 21);

// ↵ 42

mockedAdd(9000, 1);

// ↵ 9001 (😱 OVER 9000)

mockedAdd.hasBeenCalled();

// ↵ true

mockedAdd.hasBeenCalledWith(2000, 12);

// ↵ false

mockedAdd.hasBeenCalledWith(21, 21);

// ↵ true

mockedAdd.hasBeenCalledTimes;

// ↵ 2

mockedAdd.calls;

// ↵ [[21, 21], [9000, 1]]

```

## Caveats

[Mocking is a code smell](https://medium.com/javascript-scene/mocking-is-a-code-smell-944a70c90a6a)

for tight coupling and as such a surface indication that you might be able to

improve your tests and / or underlying code. Think about whether you can isolate

your side-effects or non-deterministic functions and make your code more

modular. Mocking can be okay, for example in integration tests.

For example, the pure function `add` in [Usage](#usage) should be tested using

plain unit tests that

[assert the actual and expected output](https://medium.com/javascript-scene/rethinking-unit-test-assertions-55f59358253f).

I chose `add` to simplify the example, but it is generally a bad use-case for

mocking.