测试自定义钩子时,setup函数返回undefined

我从网上的某个地方得到了可以使用的代码。usePrevious的代码如下所示:

export const usePrevious = (value) => {
  const ref = useRef();
  useEffect(() => {
    ref.current = value;
  }, [value]);
  return ref.current;
};

现在,我正在学习如何用笑话和酶来测试反应。所以,我试图测试usePrevious,但遇到了一些问题。以下是我的测试用例:

import React from 'react';
import { render } from 'enzyme';

import { usePrevious } from './customHooks';

const Component = ({ children, value }) => children(usePrevious(value));
const setup = (value) => {
  let returnVal = '';
  render(
    <Component value={value}>
      {
        (val) => {
          returnVal = val;
          return null;
        }
      }
    </Component>,
  );
  return returnVal;
};

describe('usePrevious', () => {
  it('returns something', () => {
    const test1 = setup('test');
    const test2 = setup(test1);
    expect(test2).toBe('test');
  });
});

当测试执行完成时,我得到以下错误:

Expected: 'test', Received: undefined

谁能告诉我为什么我没有定义,这是在react中测试定制Hoook的正确方法吗?

在@Dmitrii G的评论中提出建议后,我更改了代码以重新呈现该组件(之前我正在重新安装该组件)。

以下是更新后的代码:

import React from 'react';
import PropTypes from 'prop-types';
import { shallow } from 'enzyme';

import { usePrevious } from './customHooks';

const Component = ({ value }) => {
  const hookResult = usePrevious(value);
  return (
    <div>
      <span>{hookResult}</span>
      <span>{value}</span>
    </div>
  );
};

Component.propTypes = {
  value: PropTypes.string,
};

Component.defaultProps = {
  value: '',
};


describe('usePrevious', () => {
  it('returns something', () => {
    const wrapper = shallow(<Component value="test" />);
    console.log('>>>>> first time', wrapper.find('div').childAt(1).text());
    expect(wrapper.find('div').childAt(0).text()).toBe('');

    // Test second render and effect
    wrapper.setProps({ value: 'test2' });
    console.log('>>>>> second time', wrapper.find('div').childAt(1).text());
    expect(wrapper.find('div').childAt(0).text()).toBe('test');
  });
});

但我还是犯了同样的错误

Expected: "test", Received: ""

引入settimeout时,测试通过:

import React from 'react';
import PropTypes from 'prop-types';
import { shallow } from 'enzyme';

import { usePrevious } from './customHooks';

const Component = ({ value }) => {
  const hookResult = usePrevious(value);
  return <span>{hookResult}</span>;
};

Component.propTypes = {
  value: PropTypes.string,
};

Component.defaultProps = {
  value: '',
};


describe('usePrevious', () => {
  it('returns empty string when component is rendered first time', () => {
    const wrapper = shallow(<Component value="test" />);
    setTimeout(() => {
      expect(wrapper.find('span').text()).toBe('');
    }, 0);
  });
  it('returns previous value when component is re-rendered', () => {
    const wrapper = shallow(<Component value="test" />);
    wrapper.setProps({ value: 'test2' });
    setTimeout(() => {
      expect(wrapper.find('span').text()).toBe('test');
    }, 0);
  });
});

我不太喜欢使用settimeout,所以我觉得我可能犯了一些错误。如果有人知道一个不使用settimeout的解决方案,请随时在这里发布。非常感谢。