用Jest酶测试React Reducer

import reducer from './reducer';

test('initial state', () => {
  const initialState = { count: 0 };
  expect(reducer(undefined, {})).toEqual(initialState);
});

import reducer from './reducer';
import { increment } from './actions';

test('increment action', () => {
  const initialState = { count: 0 };
  const action = increment();
  const nextState = reducer(initialState, action);
  expect(nextState.count).toBe(1);
});

import reducer from './reducer';
import { increment, decrement } from './actions';

test('multiple actions', () => {
  const initialState = { count: 0 };
  const action1 = increment();
  const action2 = decrement();
  const nextState1 = reducer(initialState, action1);
  const nextState2 = reducer(nextState1, action2);
  expect(nextState2.count).toBe(0);
});