React Native测试按钮按下

Question

我正在尝试从React Native的Button元素调用组件方法进行测试。

由于某种原因，除非我同时执行以下两个步骤，否则测试会失败。

wrapper.find(Button).first().props().onPress();
wrapper.find(Button).first().simulate('press');

如果我将其中一行注释掉，测试就会失败，指示expect(instance.toggleEmailPasswordModal).toHaveBeenCalled();失败。

这是我的组件：

import React, { Component } from 'react';
import { Button, SafeAreaView, Text } from 'react-native';

import EmailPasswordModal from './EmailPasswordModal/EmailPasswordModal';

class Login extends Component {
  state = {
    emailPasswordModalVisible: false,
  };

  toggleEmailPasswordModal = () => {
    console.log('TOGGLED!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!');
    const { emailPasswordModalVisible } = this.state;
    this.setState({ emailPasswordModalVisible: !emailPasswordModalVisible });
  };

  render() {
    const { emailPasswordModalVisible } = this.state;
    return (
      <SafeAreaView>

        <EmailPasswordModal
          visible={ emailPasswordModalVisible }
          close={ this.toggleEmailPasswordModal }
        />

        <Text>Login Screen!</Text>

        <Button
          onPress={ this.toggleEmailPasswordModal }
          title="Login with Email and Password"
          color="#841584"
          accessibilityLabel="Login with Email and Password"
        />

      </SafeAreaView>
    );
  }
}

export default Login;

这是我的测试：

import React from 'react';
import ShallowRenderer from 'react-test-renderer/shallow';
import { shallow } from 'enzyme';
import { Button } from 'react-native';

import Login from './Login';

describe('Login Screen', () => {
  describe('Snapshot Tests', () => {
    it('renders the screen with default state', () => {
      const renderer = new ShallowRenderer();
      const props = {};

      renderer.render(<Login { ...props } />);
      expect(renderer.getRenderOutput()).toMatchSnapshot();
    });
  });

  describe('Functional Tests', () => {
    it('calls the toggleEmailPasswordModal method', () => {
      const wrapper = shallow(<Login />);
      const instance = wrapper.instance();
      jest.spyOn(instance, 'toggleEmailPasswordModal');
      wrapper.find(Button).first().props().onPress();
      wrapper.find(Button).first().simulate('press');
      expect(instance.toggleEmailPasswordModal).toHaveBeenCalled();
    });
  });
});

奇怪的是，当测试运行时，由于组件中的日志记录，输出会显示“TOGGLED!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!”两次。

然而，如果我将 expect 改为：

expect(instance.toggleEmailPasswordModal).toHaveBeenCalledTimes(1);

测试通过。 如果我将 expect 改为：

expect(instance.toggleEmailPasswordModal).toHaveBeenCalledTimes(2);

测试失败，显示toggleEmailPasswordModal仅被调用了1次。

为什么我需要这两行代码：wrapper.find(Button)...？我从未见过其他测试需要同时使用这两行代码。

谢谢， Justin

更新：

我将我的测试更新如下：

it('calls the toggleEmailPasswordModal method', () => {
  const wrapper = shallow(<Login />);
  const instance = wrapper.instance();
  jest.spyOn(instance, 'toggleEmailPasswordModal');
  wrapper.find(Button).first().props().onPress();
  wrapper.find(Button).first().simulate('press');
  expect(instance.toggleEmailPasswordModal).toHaveBeenCalled();

  // I ADDED THIS SECTION HERE
  expect(instance.state.emailPasswordModalVisible).toBe(true);
});

测试失败是因为instance.state.emailPasswordModalVisible = false。这很奇怪，因为toggleEmailPasswordModal显然被调用了。然而，由于我怀疑它实际上被调用了两次，因此我将测试更新如下：

it('calls the toggleEmailPasswordModal method', () => {
  const wrapper = shallow(<Login />);
  const instance = wrapper.instance();
  jest.spyOn(instance, 'toggleEmailPasswordModal');
  wrapper.find(Button).first().props().onPress();

  // CHANGES START HERE
  // wrapper.find(Button).first().simulate('press');
  // expect(instance.toggleEmailPasswordModal).toHaveBeenCalled();
  expect(instance.state.emailPasswordModalVisible).toBe(true);
});

猜猜看？测试通过了。所以，显然两次调用wrapper.find...函数确实是调用了toggleEmailPasswordModal方法两次。那么，如果我不调用两次，为什么它会失败地检测到它呢？为什么它错误地认为该方法只被调用了一次？

- Justin Noel

Answer 1

我终于有了答案。根据Jest spyOn function called，我需要执行instance.forceUpdate()将spy附加到组件上。

it('calls the toggleEmailPasswordModal method', () => {
  const wrapper = shallow(<Login />);
  const instance = wrapper.instance();
  const spy = jest.spyOn(instance, 'toggleEmailPasswordModal');

  // This is added per https://dev59.com/bFcP5IYBdhLWcg3wLnRC#44778519
  instance.forceUpdate();
  wrapper.find(Button).first().props().onPress();

  expect(spy).toHaveBeenCalledTimes(1);
  expect(instance.state.emailPasswordModalVisible).toBe(true);
});

现在，测试通过了！

- Justin Noel

Answer 2

另一个寻找活动的例子：

const button = screen.getByTestId('...');
act(() => {
  fireEvent.press(button);
});
expect(hookFn).toBeCalled();

- Nagibaba