jest-mock-curry-fn
v0.0.3
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jest-mock-curry-fn
Easier testing with curry functions + jest 🧪
Who's it for?
- You use curried functions (see more: Curry and Function Composition)
- You would like to mock away certain curried functions (eg. XHR calls) for ease of testing
- You need unit tests to assert that these curried functions are called correctly
- You don't want to write so much setup code for testing curried functions
Scenario
// 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!
- 1st mock:
Usage
// 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
API
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
Tips:
- For most use cases, you will only need to use
headMockFn
andexpectMockFnsCalledWith()
. - For other advanced cases, can access individual
mockFns
to modify underlyingjest.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.