Jest.js如何测试另一个函数内部被调用的函数 [英] Jestjs how to test function being called inside another function

问题描述

对于测试，我使用jest和react-test-renderer.测试应该很简单，但是我很难找到合适的例子.我试图做类似的事情(通常我将功能保存在单独的文件中):

For testing I use jest and react-test-renderer. It should be simple to test, however I have a hard time finding the proper example. I have tried to do something like that (in general I keep the functions in separate files):

utils.js

export const childFunction = () => 'something';    
const parentFunction = () => childFunction();
export default parentFunction;

utils.test.js

utils.test.js

import parentFunction from './utils.js';


it('childFunction should be called', () => {
 const childFunction = jest.fn();
 parentFunction();
 expect(childFunction).toBeCalled();
})

片段 const childFunction = jest.fn(); 绝对不起作用.调用时，parentFunction的主体仅关心其自身的作用域.但是，如果我导入childFunction并执行 jest.mock(childFunction)，它也将不起作用，因为jest.mock需要一个字符串，一个模块的url，而不是函数本身.

The fragment const childFunction = jest.fn(); definitely won't work. While calling, parentFunction's body cares only about its own scope. But it also won't work if I import childFunction and do jest.mock(childFunction), because jest.mock needs a string, a url to a module, and not the function itself.

上面的示例不起作用，我正在寻找替代方法.但是，在使用ShallowRenderer渲染组件后，此方法有效.而且我想通过嵌套在另一个函数中的函数来实现类似的行为.

The example above doesn't work and I'm searching for an alternative. However this works after rendering the component with ShallowRenderer. And I'd like to achieve a similar behaviour with a function nested inside another function.

class Component extends React.Component {
 componentDidMount() {parentFunction()}
 render() {...}
}

const renderer = new ShallowRenderer();
describe("testing parentFunction", () => {
  renderer.render(<Component/>);
  it("parentFunction should be called", () => {
    expect(parentFunction).toBeCalled();
  });
});

推荐答案

如果未将函数作为对象方法调用，则无法监视函数调用.

There's no way to spy on function call if a function isn't called as object method.

如此答案中所述，由于ES模块的工作方式，只有在以下情况下才可能监视或模拟函数:它是从一个模块导出的，并在另一个模块中使用.这样，就可以在模块*对象上对其进行监视，或者使用jest.mock对其进行模拟.

As explained in this answer, due to how ES modules work, it's possible to spy or mock a function only if it was exported from a module and is used in another module. This way it can be spied on module * object, or be mocked with jest.mock.

如果不是这种情况，则应进行间接测试:

If this isn't the case, it should be tested indirectly:

expect(childFunction()).toBe('something');
expect(parentFunction()).toBe('something');

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