用 Jest 模拟 React 自定义钩子 [英] Mocking React custom hook with Jest

问题描述

在对 React 组件进行单元测试时，我需要模拟我的自定义钩子.我已经阅读了一些关于这个简单任务的教程和 stackoverflow 答案，但没有正确实现它.

I need to mock my custom hook when unit testing React component. I have read few tutorials and stackoverflow answers to this simple task, but without luck to implement it correctly.

我最简单的单一测试设置如下:

My simplest possible setup for single test is as following:

// TestComponent.js

import React from "react";
import useTest from "./useTest";

const TestComponent = () => {
  const { state } = useTest("initial_value");

  return <div>{state}</div>;
};

export default TestComponent;

// useTest.jsx - simple custom hook

import React, { useState } from "react";

const useTest = (initialState) => {
  const [state] = useState(initialState);
  return { state };
};

export default useTest;

// TestComponent.test.jsx - my test case

import React from "react";
import { render } from "@testing-library/react";
import TestComponent from "./TestComponent";

jest.mock("./useTest", () => ({
  useTest: () => "mocked_value",
}));

test("rendertest", () => {
  const component = render(<TestComponent />);
  expect(component.container).toHaveTextContent("mocked_value");
});

所以我试图模拟 useTest 自定义钩子以返回mocked_value"，而不是initial_value"；来自真正的自定义钩子.但上面的代码只是给了我这个错误:

So I trying to mock useTest custom hook to return "mocked_value", instead of "initial_value" from real custom hook. But above code just gives me this error:

TypeError: (0 , _useTest.default) is not a function

      3 | 
      4 | const TestComponent = () => {
    > 5 |   const { state } = useTest("initial_value");
        |                     ^
      6 | 
      7 |   return <div>{state}</div>;
      8 | };

我也试过:

import useTest from './useTest';
// ...
jest.spyOn(useTest, "useTest").mockImplementation(() => "mocked_value");

import useTest from './useTest';
// ...
jest.spyOn(useTest, "useTest").mockReturnValue("mocked_value");

但两者都给我错误 无法监视 useTest 属性，因为它不是函数；.

如何实施此测试?

推荐答案

我在回答自己.这样它的工作方式:

I'm answering to myself. This way it's working:

jest.mock("./useTest", () => ({
  useTest: () => ({ state: 'mocked_value' }),
}));

如果我想在自定义钩子中使用默认导出:

And if I want to use default export in custom hook:

jest.mock("./useTest", () => ({
  __esModule: true,
  default: () => ({ state: 'mocked_value' }),
}));

另外，如果我还想在我的钩子中使用 setState 方法并导出它，我可以像这样模拟它:

Also, if I want to also use setState method in my hook and export it, I can mock it like this:

const mockedSetState = jest.fn();

jest.mock("./useTest", () => ({
  useTest: () => ({ state, setState: mockedSetState }),
}));

现在可以检查 setState 是否被调用过一次:

And now it's possible to check if setState has been called once:

expect(mockedSetState).toHaveBeenCalledTimes(1);

这篇关于用 Jest 模拟 React 自定义钩子的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！