Examples of Snapshot testing a Redux Saga

sagas-example.js

/**
 * Basic saga that revokes session and redirects to /login
 * each time a LOGOUT action is dispatched
 */
function* logoutSaga() {
  while (true) {
    yield take(LOGOUT)
    yield put(revokeSession())
    yield put(redirect('/login'))
  }
}

/**
 * Testing this with snapshot testing
 */
it('should revoke session and redirect to login', () => {
  const gen = logoutSaga()
  
  // Iterate 4 times, to ensure `done` is still false after the first loop
  for (let i=0; i < 4; ++i) {
    expect(gen.next()).toMatchSnapshot()
  }
})

/**
 * Bit more complex saga, that expects a returned value
 */
function* fetchUserSaga() {
  while (true) {
    yield take(FETCH_USER)
    try {
      const user = yield call(Api.fetchUser)
      yield put({ type: FETCH_USER_SUCCESS, payload: user })
    } catch (e) {
      yield put({ type: FETCH_USER_FAIL, error: true, payload: e })
    }
  }
}

it('should dispatch a FETCH_USER_SUCCESS', () => {
  const gen = fetchUserSaga()
  
  // Take FETCH_USER
  expect(gen.next()).toMatchSnapshot()
  
  // Call API
  expect(gen.next({ id: 42, name: 'John Doe' })).toMatchSnapshot()
  
  // Dispatch FETCH_USER_SUCCESS
  expect(gen.next()).toMatchSnapshot()
  
  // Loop
  expect(gen.next()).toMatchSnapshot()
})

it('should dispatch a FETCH_USER_FAIL', () => {
  const gen = fetchUserSaga()
  
  // Take FETCH_USER
  expect(gen.next()).toMatchSnapshot()
  
  // Call API
  expect(gen.throw({ code: 404 })).toMatchSnapshot()
  
  // Dispatch FETCH_USER_FAIL
  expect(gen.next()).toMatchSnapshot()
  
  // Loop
  expect(gen.next()).toMatchSnapshot()
})