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https://github.com/nossbigg/jest-mock-curry-fn
Easier testing with curry functions + jest 🧪
https://github.com/nossbigg/jest-mock-curry-fn
curried curry currying function jest mock testing
Last synced: 4 months ago
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Easier testing with curry functions + jest 🧪
- Host: GitHub
- URL: https://github.com/nossbigg/jest-mock-curry-fn
- Owner: nossbigg
- Created: 2021-03-14T16:11:04.000Z (almost 4 years ago)
- Default Branch: main
- Last Pushed: 2021-06-07T05:55:11.000Z (over 3 years ago)
- Last Synced: 2024-10-04T17:50:06.470Z (4 months ago)
- Topics: curried, curry, currying, function, jest, mock, testing
- Language: TypeScript
- Homepage:
- Size: 160 KB
- Stars: 8
- Watchers: 2
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
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README
# jest-mock-curry-fn
[](https://badge.fury.io/js/jest-mock-curry-fn)
Easier testing with curry functions + jest 🧪
# Who's it for?
1. You use **curried functions** (see more: [Curry and Function Composition](https://medium.com/javascript-scene/curry-and-function-composition-2c208d774983))
1. You would like to **mock away certain curried functions** (eg. XHR calls) for ease of testing
1. You need unit tests to assert that these **curried functions are called correctly**
1. You **don't want to write so much setup code** for testing curried functions
# Scenario
```javascript
// makeName.ts
export const makeName = (name) => {
const prefix = stringPrefixer('first')('second')
const result = `${prefix} ${name}`
return result
}
// stringPrefixer.ts
export const stringPrefixer = (first) => (second) => {
return `${first}-${second}`
}
```
Scenario:
- System Under Test is `makeName()`
- When `makeName()` is called (eg. `makeName('whee!)`),
- Then we expect that `stringPrefixer` has been called with:
- 1st mock: `('first')`
- 2nd mock: `('second')`
- Returned value: `hey! whee!`
# Usage
```javascript
// 1. import makeMockCurryFn()
import { makeMockCurryFn } from 'jest-mock-curry-fn'
// 2. import function under test
import { makeName } from './makeName'
// 3. import underlying function that requires mocking
import * as stringPrefixerImport from './stringPrefixer'
test('asserts curry fn is called', () => {
// 4. create mocked curry fn
const mockStringPrefixerFn = makeMockCurryFn({
nCurriedFns: 2,
tailFnReturnValue: 'hey!',
})
// 5. mock stringPrefixer() usage
jest
.spyOn(stringPrefixerImport, 'stringPrefixer')
.mockImplementation(mockStringPrefixerFn.headMockFn)
// 6. trigger usage of top-level function
const result = makeName('whee!')
// 7. assert curry fn calls
mockStringPrefixerFn.expectMockFnsCalledWith('first')('second')
// 8. assert return value
expect(result).toEqual('hey! whee!')
})
```
See more: [sampleUsage.test.ts](/src/test/sampleUsage/sampleUsage.test.ts)
# API
```javascript
const options = {
// required: number of nested curried fns, must be >= 1
nCurriedFns: 2,
// required: return value of last curried fn
tailFnReturnValue: 'hey!',
}
const mockCurryFn = makeMockCurryFn(options)
const {
// to assert curried fns to be called with certain arguments
expectMockFnsCalledWith,
// head fn to be used as the entrypoint for the curried fn to be used
headMockFn,
// tail fn to be called at the end of the chained curried fns
tailMockFn,
// list of mock fns (chained together to work in curry scenario)
mockFns,
// initial options used to initialize current curryFn
options,
} = mockCurryFn
```
See more: [makeMockCurryFn.ts](/src/makeMockCurryFn/makeMockCurryFn.ts)
Tips:
- For most use cases, you will only need to use `headMockFn` and `expectMockFnsCalledWith()`.
- For other advanced cases, can access individual `mockFns` to modify underlying `jest.fn()`s to suit your scenario.
- Eg. Asserting specific mock function not to be called with certain argument.
- Eg. Modifying `tailMockFn` to return different return value depending on how the function is called.