如何使用 useReducer 钩子测试组件？

Question

减速机

// src/reducers/FooReducer.js

export function FooReducer(state, action) {
  switch (action.type) {
    case 'update': {
      return action.newState;
    }
// ... other actions
    default:
      throw new Error('Unknown action type');
  }
}

组件

// src/components/BarComponent.js

export function BarComponent() {
  const [state, dispatch] = useReducer(FooReducer, []);

  return (
    {state.map((item) => (<div />))}
  );
}

测试

// src/components/BarComponent.test.js

it('should render as many divs as there are items', () => {
  act(() => {
    const { result } = renderHook(() => useReducer(FooReducer, [1]));
    const [, dispatch] = result.current;
    wrapper = mount(<BarComponent />);
    dispatch({type: 'update', newState: [1, 2, 3]});
  });

  expect(wrapper.find(div)).toHaveLength(3);
});

上面的测试示例不起作用，但可以用来演示我正在努力实现的目标。并且实际上会呈现 0 div，因为组件中声明的初始状态包含 0 个项目。

我将如何修改 reducer 的状态或更改它部署时用于测试目的的 initialState？
我已经习惯了在多个组件中使用 Redux reducer，但是 useReducer 需要一个传递的 initialState... 这引发了一个问题：React-hook 的 reducer 是否可以通过多个组件作为单个实例使用，或者它会始终是 2 个单独的实例吗？

Answer 1

在您的示例中，您正在尝试同时测试两件事，这最好作为单独的测试进行：针对您的减速器的单元测试，以及组件使用减速器的组件测试。

How would I go about modifying a reducer's state or changing the initialState it is deployed with for testing purposes?

与 Redux reducer 类似，您的 reducer 很容易进行单元测试，因为您将其导出为纯函数。只需将您的初始状态传递给 state 参数，然后将您的操作传递给 action:

it('returns new state for "update" type', () => {
  const initialState = [1];
  const updateAction = {type: 'update', newState: [1, 2, 3] };
  const updatedState = fooReducer(initialState, udpateAction);
  expect(updatedState).toEqual([1, 2, 3]);
});

如果您愿意，也可以在 useReducer 的上下文中进行测试：

it('should render as many divs as there are items', () => {
  act(() => {
    const { result } = renderHook(() => useReducer(FooReducer, [1]));
    const [state, dispatch] = result.current;
    dispatch({type: 'update', newState: [1, 2, 3]});
  });

  expect(state).toEqual([1, 2, 3]);
  // or expect(state).toHaveLenth(3) if you prefer
});

I am used to Redux reducers being used throughout multiple components, but useReducer needs a passed initialState... which raises the question: Is react-hook's reducer usable through multiple components asa single instance or will it always be 2 separate instances?

以下是 useReducer 与 Redux 的不同之处：您可以重用 reducer 本身，但是如果您有多个 useReducer，则 state 和 dispatch 会从每一个，以及初始状态，都是单独的实例。

为了测试 BarComponent 在 reducer 更新时是否更新，您需要一种从组件内部触发 dispatch 的方法，因为您是在组件内部调用 useReducer。这是一个例子：

export function BarComponent() {
  const [state, dispatch] = useReducer(FooReducer, []);

  const handleUpdate = () => dispatch({type: 'update', newState: [1, 2, 3]})

  return (
    <>
      {state.map((item) => (<div key={item} />))}
      <button onClick={handleUpdate}>Click to update state</button>
    </>
  );
}

it('should render as many divs as there are items', () => {
  wrapper = mount(<BarComponent />);

  expect(wrapper.find('div')).toHaveLength(0);

  wrapper.find('button').simulate('click');

  expect(wrapper.find('div')).toHaveLength(3);
});

这可能不太现实，因为我在组件本身中对新数组进行了硬编码，但希望它能给您带来灵感！

如何使用 useReducer 钩子测试组件？

How test a component using the useReducer hook?

reactjs

enzyme

react-hooks

react-hooks-testing-library

减速机

组件

测试