嘲笑事件发射器对象的发射事件(表达) [英] jest test emitting events for eventemitter objects (express)

问题描述

试图从针对事件发射器对象(http)的最好的测试发射事件不能解决 express .

假设以下nodejs代码

assume the following nodejs code

// server.js

const express = require("express");
const app = express();

const server = app.listen(8080,'127.0.0.1')
  .on("error", err => {
    // ...
  });

module.exports = server;

如何使用笑话编写测试以发出http错误"事件(以覆盖错误事件处理程序)?

how to write a test using jest to emit the http "error" event (to cover the error event handler)?

我尝试过:

// server.test.js

it("should handle error", () => {
  jest.mock("express", () => () => ({
    listen: jest.fn().mockReturnThis(),
    on: jest.fn().mockImplementationOnce((event, handler) => {
      handler(new Error("network"));
    })
  }))
  const express = require("express");
  const app = express();
  const appListenSpy = jest.spyOn(app, "listen")
  require("./server");
  expect(appListenSpy).toBeCalledTimes(1);
  expect(app.listen).toBeCalledWith(8080,'127.0.0.1');
  expect(app.on).toBeCalledWith("error", expect.any(Function));
});

但是运行测试时我会得到什么

but what i get when running the test

 ● server › should handle listen error

    expect(jest.fn()).toBeCalledTimes(expected)

    Expected number of calls: 1
    Received number of calls: 0

    > 29 |     expect(appListenSpy).toBeCalledTimes(1);

推荐答案

您不能在函数范围内使用jest.mock.应该在模块范围内使用.而不是在测试用例函数中使用jest.mock，您应该使用 jest .doMock(moduleName，factory，options)

You can't use jest.mock in the function scope. It should be used in the module scope. Instead of using jest.mock inside the test case function, you should use jest.doMock(moduleName, factory, options)

例如 server.js:

const express = require('express');
const app = express();

const server = app.listen(8080, '127.0.0.1').on('error', (err) => {
  console.log(err);
});

module.exports = server;

server.test.js:

describe('60451082', () => {
  it('should pass', () => {
    const mError = new Error('network');
    const appMock = {
      listen: jest.fn().mockReturnThis(),
      on: jest.fn().mockImplementationOnce((event, handler) => {
        handler(mError);
      }),
    };
    jest.doMock('express', () => jest.fn(() => appMock));
    const logSpy = jest.spyOn(console, 'log');
    const express = require('express');
    require('./server');
    expect(express).toBeCalledTimes(1);
    expect(appMock.listen).toBeCalledWith(8080, '127.0.0.1');
    expect(appMock.on).toBeCalledWith('error', expect.any(Function));
    expect(logSpy).toBeCalledWith(mError);
  });
});

单元测试结果覆盖率100％:

Unit test results with 100% coverage:

 PASS  stackoverflow/60451082/server.test.js
  60451082
    ✓ should pass (19ms)

  console.log node_modules/jest-environment-enzyme/node_modules/jest-mock/build/index.js:866
    Error: network
        at Object.<anonymous> (/Users/ldu020/workspace/github.com/mrdulin/react-apollo-graphql-starter-kit/stackoverflow/60451082/server.test.js:3:20)
        at Object.asyncJestTest (/Users/ldu020/workspace/github.com/mrdulin/react-apollo-graphql-starter-kit/node_modules/jest-jasmine2/build/jasmineAsyncInstall.js:100:37)
        at resolve (/Users/ldu020/workspace/github.com/mrdulin/react-apollo-graphql-starter-kit/node_modules/jest-jasmine2/build/queueRunner.js:43:12)
        at new Promise (<anonymous>)
        at mapper (/Users/ldu020/workspace/github.com/mrdulin/react-apollo-graphql-starter-kit/node_modules/jest-jasmine2/build/queueRunner.js:26:19)
        at promise.then (/Users/ldu020/workspace/github.com/mrdulin/react-apollo-graphql-starter-kit/node_modules/jest-jasmine2/build/queueRunner.js:73:41)
        at process._tickCallback (internal/process/next_tick.js:68:7)

-----------|---------|----------|---------|---------|-------------------
File       | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
-----------|---------|----------|---------|---------|-------------------
All files  |     100 |      100 |     100 |     100 |                   
 server.js |     100 |      100 |     100 |     100 |                   
-----------|---------|----------|---------|---------|-------------------
Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        4.444s, estimated 10s

源代码: https://github.com/mrdulin/react-apollo-graphql-starter-kit/tree/master/stackoverflow/60451082

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