fp-ts-jest-matchers

Jest Matchers for fp-ts

This library provides Jest matchers to nicely test code based on fp-ts. Currently it provides matchers for Option and Either.

Installation

First add the dependency to your project:

yarn add --dev fp-ts-jest-matchers

Then make sure this package is loaded by Jest. If you have a file setupTests.ts, you can include it there:

import 'fp-ts-jest-matchers'

If not, you may need to add this to your Jest config:

"jest": {
  "setupFilesAfterEnv": ["fp-ts-jest-matchers"]
}

Usage

After installation, you can now write assertions like these in your test:

import * as O from 'fp-ts/lib/Option'
import * as E from 'fp-ts/lib/Either'
import * as A from 'fp-ts/lib/Array'
 
it('can test fp-ts options', () => {
    // Expect an option to be 'none':
    expect(O.none.toBeNone()
 
    // Expect an option to be 'some' with any value:
    expect(O.some('value')).toBeSome()
 
    // Expect an option to be 'some' with a specific value:
    expect(O.some('value')).toBeSome('value')
 
    // Use custom Eq for testing the value:
    expect(O.some(['a', 'b'])).toBeSome(['a', 'b'], A.getEq(eqString))
})
 
it('can test fp-ts eithers', () => {
    // Expect an either to be a left:
    expect(E.left('left value')).toBeLeft()
 
    // Expect an either to be a left with a specific value:
    expect(E.left('left value')).toBeLeft('left value')
 
    // Use custom Eq for testing the value:
    expect(E.left(['a', 'b'])).toBeLeft(['a', 'b'], A.getEq(eqString))
 
    // Expect an either to be a right:
    expect(E.right('right value')).toBeRight()
 
    // Expect an either to be a right with a specific value:
    expect(E.right('right value')).toBeRight('right value')
 
    // Use custom Eq for testing the value:
    expect(E.right(['a', 'b'])).toBeRight(['a', 'b'], A.getEq(eqString))
})