testing

Small context wrapper simplify your mocking and testing.

We recommend to use uvu as helper library for test description, as it could be used in any runtime (and even browser!) and super fast. To clarify, with uvu you allow to run your test files with node / deno / bun / graalvm / esbuild-kit/tsx and browser just out of the box. But @reatom/testing is not coupled to uvu, you could use any testing framework.

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

import { test } from 'uvu'
import * as assert from 'uvu/assert'
import { action, atom } from '@reatom/core'
import { spyChange } from '@reatom/hooks'
import { createTestCtx } from '@reatom/testing'

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

  assert.is(track.calls.length, 1)
  assert.is(track.lastInput(), 0)

  add(ctx, 10)
  assert.is(track.calls.length, 2)
  assert.is(track.lastInput(), 10)

  ctx.mockAction(add, () => 100)
  add(ctx, 10)
  assert.is(track.calls.length, 3)
  assert.is(track.lastInput(), 110)

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

  unmock()
  add(ctx, 10)
  assert.is(track.calls.length, 5)
  assert.is(track.lastInput(), 223)
})

test.run()