Jest.js 如何测试一个依赖于useContext钩子的react组件?

chy5wohz  于 2023-01-22  发布在  Jest
关注(0)|答案(8)|浏览(238)

我有一个使用useContext的组件,它的输出依赖于上下文中的值。

import React, { useContext } from 'react';

const MyComponent = () => {
  const name = useContext(NameContext);

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

当使用react和jest快照中的shallow renderer测试这个组件时,如何更改NameContext的值?

vs91vp4v

vs91vp4v1#

一般来说,使用钩子不会改变测试策略,更大的问题实际上不是钩子,而是上下文的使用,这会使事情变得有点复杂。
有很多方法可以实现这一点,但我发现的唯一一种适用于'react-test-renderer/shallow'的方法是注入一个mock钩子:

import ShallowRenderer from 'react-test-renderer/shallow';

let realUseContext;
let useContextMock;
// Setup mock
beforeEach(() => {
    realUseContext = React.useContext;
    useContextMock = React.useContext = jest.fn();
});
// Cleanup mock
afterEach(() => {
    React.useContext = realUseContext;
});

test("mock hook", () => {
    useContextMock.mockReturnValue("Test Value");
    const element = new ShallowRenderer().render(
        <MyComponent />
    );
    expect(element.props.children).toBe('Test Value');
});

不过,这有点脏,并且是特定于实现的,因此如果您能够在使用浅渲染器方面做出妥协,还有一些其他选项可用:

非浅渲染

如果不是浅呈现,可以将组件 Package 在上下文提供器中以注入所需的值:

import TestRenderer from 'react-test-renderer';

test("non-shallow render", () => {
    const element = new TestRenderer.create(
        <NameContext.Provider value="Provided Value">
            <MyComponent />
        </NameContext.Provider>
    );
    expect(element.root.findByType("div").children).toEqual(['Provided Value']);
});

(免责声明:这 * 应该 * 工作,但当我测试它,我击中了一个错误,我认为这是一个问题,在我的设置)

使用酶和潜水进行浅渲染

正如@skyboyer评论的那样,enzyme的浅层渲染器支持.dive,允许你对浅层渲染组件的一部分进行深层渲染:

import { shallow } from "./enzyme";

test("enzyme dive", () => {
    const TestComponent = () => (
        <NameContext.Provider value="Provided Value">
            <MyComponent />
        </NameContext.Provider>
    );
    const element = shallow(<TestComponent />);
    expect(element.find(MyComponent).dive().text()).toBe("Provided Value");
});

使用ReactDOM

最后,Hooks FAQ有一个使用ReactDOM测试钩子的例子,它也能正常工作。自然,使用ReactDOM意味着这也是一个深度渲染,而不是浅度渲染。

let container;
beforeEach(() => {
    container = document.createElement('div');
    document.body.appendChild(container);
});

afterEach(() => {
    document.body.removeChild(container);
    container = null;
});

test("with ReactDOM", () => {
    act(() => {
        ReactDOM.render((
            <NameContext.Provider value="Provided Value">
                <MyComponent />
            </NameContext.Provider>
        ), container);
    });

    expect(container.textContent).toBe("Provided Value");
});
gijlo24d

gijlo24d2#

我尝试使用Enzyme + .dive,但是当潜水时,它不能识别上下文属性,它得到默认的属性。实际上,这是Enzyme团队已知的问题。同时,我想出了一个更简单的解决方案,包括创建一个自定义钩子来返回useContext和您的上下文,并在测试中模拟这个自定义钩子的返回:
AppContext.js -创建上下文。

import React, { useContext } from 'react';

export const useAppContext = () => useContext(AppContext);

const defaultValues = { color: 'green' };
const AppContext = React.createContext(defaultValues);

export default AppContext;

App.js - 提供上下文

import React from 'react';
import AppContext from './AppContext';
import Hello from './Hello';

export default function App() {
  return (
    <AppContext.Provider value={{ color: 'red' }}>
      <Hello />
    </AppContext.Provider>
  );
}

Hello.js -使用上下文

import React from 'react';
import { useAppContext } from './AppContext';

const Hello = props => {
  const { color } = useAppContext();
  return <h1 style={{ color: color }}>Hello {color}!</h1>;
};

export default Hello;

js-使用Enzyme shallow测试useContext

import React from 'react';
import { shallow } from 'enzyme';
import * as AppContext from './AppContext';

import Hello from './Hello';

describe('<Hello />', () => {
  test('it should mock the context', () => {
    const contextValues = { color: 'orange' };
    jest
      .spyOn(AppContext, 'useAppContext')
      .mockImplementation(() => contextValues);
    const wrapper = shallow(<Hello />);
    const h1 = wrapper.find('h1');

    expect(h1.text()).toBe('Hello orange!');
  });
});

检出完整的中型文章https://medium.com/7shifts-engineering-blog/testing-usecontext-react-hook-with-enzyme-shallow-da062140fc83

b4lqfgs4

b4lqfgs43#

或者,如果您正在单独测试组件,而没有挂载父组件,您可以简单地模拟useContext:

jest.mock('react', () => {
  const ActualReact = jest.requireActual('react')
  return {
    ...ActualReact,
    useContext: () => ({ }), // what you want to return when useContext get fired goes here
  }
})
eblbsuwk

eblbsuwk4#

为了完成上面公认的答案,对于非浅呈现,我稍微调整了代码,使其简单地用上下文包围组件

import { mount } from 'enzyme';
import NameContext from './NameContext';

test("non-shallow render", () => {
    const dummyValue = {
      name: 'abcd',
      customizeName: jest.fn(),
      ...
    }; 
    const wrapper = mount(
        <NameContext.Provider value={dummyValue}>
            <MyComponent />
        </NameContext.Provider>
    );

    // then use  
    wrapper.find('...').simulate('change', ...);
    ...
    expect(wrapper.find('...')).to...;
});
cunj1qz1

cunj1qz15#

旧职位,但如果它帮助某人,这就是我如何得到它的工作

import * as React from 'react';
import { shallow } from 'enzyme';

describe('MyComponent', () => {
  it('should useContext mock and shallow render a div tag', () => {
    jest.spyOn(React, 'useContext').mockImplementation(() => ({
      name: 'this is a mock context return value'
    }));

    const myComponent = shallow(
      <MyComponent
        props={props}
      />).dive();

    expect(myComponent).toMatchSnapShot();
  });
});
8aqjt8rx

8aqjt8rx6#

在测试中,您需要用“上下文提供者” Package 组件。下面是一个简单的例子。
DisplayInfo组件依赖于用户上下文。

import React, { useContext } from 'react';
import { UserContext } from './contexts/UserContextProvider';

export const DisplayInfo = () => {
 const { userInfo } = useContext(UserContext);

 const dispUserInfo = () => {
   return userInfo.map((user, i) => {
    return (
     <div key={i}>
      <h1> Name: { user.name } </h1>
      <h1> Email: { user.email } </h1>
     </div>
    )
  });
 }

 return(
  <>
   <h1 data-testid="user-info"> USER INFORMATION </h1>
   { userInfo && dispUserInfo() })
  </>
 }

export default DisplayInfo;

这是用户上下文提供程序。

import React, {useState, createContext} from 'react';

export const UserContext = createContex();

const UserContextProvider = () => {
 const [userInfo, setUserInfo] = useState([]);

 const updateUserInfo = () => {
  setUserInfo([...userInfo, newData]);
 }

 const values = {
  userInfo,
  updateUserInfo
 }

 return(
  <UserContext.Provider = vlaue={values}>
   {props.children}
  </UserContext.Provider>
 )
}

export default UserContextProvider;

要测试“显示信息”组件,可能还需要使用“react-router-dom”中的“MemoryRouter”。示例如下-

import React from "react";
import { render, screen } from "@testing-library/react";
import "@testing-library/jest-dom/extend-expect";
import { DisplayInfo } from "./DisplayInfo";
import UserContextProvider from "./contexts/UserContextProvider";
import { MemoryRouter } from "react-router-dom";

describe("DisplayInfo", () => {
 describe("layout", () => {
  it("has header of user info", () => {
   render(
    <UserContextProvider>
     <DisplayInfo />
    </UserContextProvider>,
    { wrapper: MemoryRouter }
   );
   let header = screen.getByTestId('user-info');
   expect(header).toHaveTextContent(/user information/i)
  });
 });
});
fgw7neuy

fgw7neuy7#

我所做的是测试是否使用了useContext。在我的例子中,useContext返回名为dispatch的函数。
在组件中,我有:

const dispatch = useContext(...);

然后在onChange方法中:

dispatch({ type: 'edit', payload: { value: e.target.value, name: e.target.name } });

所以开始时的内部测试:

const dispatch = jest.fn();
  React.useContext = (() => dispatch) as <T>(context: React.Context<T>) => T;

然后:

it('calls function when change address input', () => {
   const input = component.find('[name="address"]');
   input.simulate('change', { target: { value: '123', name: 'address' } });

   expect(dispatch).toHaveBeenCalledTimes(1);
  });
fbcarpbf

fbcarpbf8#

我已经找到了一种很好的方法来模拟上下文,在那里我可以优雅地注入自己的值进行测试。

import React, {
  createContext,
  useContext,
  useState,
  useEffect,
} from "react";

const initState = {
  data: [],
};

export const ThingsContext = createContext(initState);

export const useThings = () => {
  const data = useContext(ThingsContext);
  if (data === undefined) {
    throw new Error("useThing must be used within a ThingsProvider");
  }
  return data;
};

export const ThingsProvider = ({
  children,
  value: { state: oState } = {},
}) => {
  const[data, setData] = useState();

  useEffect(() => {
    const getData = async () => {
      const data = await // api call;
      setData(data);
    }
    getData();
  }, []);

  return (
    <ThingsContext.Provider
      value={{ state: oState ?? state }}
    >
      {children}
    </ThingsContext.Provider>
  );
};

这样,我就可以覆盖实际状态并测试我想要的任何值。

import React from "react";
import { render, screen } from "@testing-library/react";

import { ThingsProvider } from "store/things";
import Things from "./Things";

const defaultValue = {
  state: ["pot", "kettle", "black"],
};

const renderComponent = (children, value=defaultValue) => {
  const el = render(
      <ThingsProvider value={value ?? defaultValue} >{children}</ThingsProvider>
  );
  screen.debug();
  return el;
};

describe("<Things />", () => {
  it("should render thing", () => {
    renderComponent(<Things />);
  });
  expect(screen.getByText("pot")).toBeInTheDocument();

  it("should not render thing", () => {
    renderComponent(<Things />, {state: []});
  });
  expect(screen.queryByText("pot")).not.toBeInTheDocument();
});

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