testing

Small context wrapper simplify your mocking and testing.

Installation

#

npm i @reatom/testing

Usage

#

import { createTestCtx, mockFn } from '@reatom/testing'

export interface TestCtx extends Ctx {
  mock<T>(anAtom: Atom<T>, fallback: T): Unsubscribe

  mockAction<T>(anAction: Action<any[], T>, cb: Fn<[Ctx], T>): Unsubscribe

  subscribeTrack<T, F extends Fn<[T]>>(
    anAtom: Atom<T>,
    cb?: F,
  ): F & {
    unsubscribe: Unsubscribe
    calls: ReturnType<typeof mockFn<[T], any>>['calls']
    lastInput: ReturnType<typeof mockFn<[T], any>>['lastInput']
  }
}

declare function mockFn<I extends any[], O>(
  fn?: (...input: I) => O,
): ((...input: I) => O) & {
  calls: Array<{ i: I; o: O }>
  lastInput: Fn<[], I[0]>
}

Story test

#

source↗

test('createTestCtx', async () => {
  const add = action<number>()
  const countAtom = atom((ctx, state = 0) => {
    ctx.spy(add, ({ payload }) => (state += payload))
    return state
  })
  const ctx = createTestCtx()
  const track = ctx.subscribeTrack(countAtom)

  expect(track.calls.length).toEqual(1)
  expect(track.lastInput()).toEqual(0)

  add(ctx, 10)
  expect(track.calls.length).toEqual(2)
  expect(track.lastInput()).toEqual(10)

  ctx.mockAction(add, (ctx, param) => 100)
  add(ctx, 10)
  expect(track.calls.length).toEqual(3)
  expect(track.lastInput()).toEqual(110)

  const unmock = ctx.mock(countAtom, 123)
  expect(track.calls.length).toEqual(4)
  expect(track.lastInput()).toEqual(123)
  add(ctx, 10)
  expect(track.calls.length).toEqual(4)
  expect(track.lastInput()).toEqual(123)

  unmock()
  add(ctx, 10)
  expect(track.calls.length).toEqual(5)
  expect(track.lastInput()).toEqual(223)
})