尝试测试异步函数抛出时，Jest 测试失败

Question

我有一个异步函数，我想同时测试：成功和失败。成功时函数返回一个字符串，失败时抛出。我在测试失败方面失败得很惨。这是我的代码：

• getKmlFileName.test.js

我已通过注释失败的代码禁用并将结果添加到 cmets

    'use strict';

    const path = require('path');
    const fs = require('fs');

    const getKmlFilename = require('./getKmlFileName.js');

    const createGoodFolder = () => {
      const folderPath = fs.mkdtempSync('/tmp/test-getKmlFilename-');
      const fileDescriptor = fs.openSync(path.join(folderPath, 'doc.kml'), 'w');
      fs.closeSync(fileDescriptor);
      return folderPath;
    };

    const createEmptyFolder = () => fs.mkdtempSync('/tmp/test-getKmlFilename-');

    describe('/app/lib/getKmlFilename', () => {
      // Success tests
      test('Should return a KML filename', async () => {
        const result = await getKmlFilename(createGoodFolder());
        expect(result).toMatch(/\.kml$/);
      });

      // Failure tests
      test('Should throw if no KML files in folder', () => {
        // Expected one assertion to be called but received zero assertion calls.
        // expect.assertions(1);

        // expect(function).toThrow(undefined)
        // Received value must be a function, but instead "object" was found
        //return getKmlFilename(createEmptyFolder())
        // .catch(e => expect(e).toThrow());

        // expect(string)[.not].toMatch(expected)
        // string value must be a string.
        // Received:
        // object:
        // [Error: No valid KML file in /tmp/test-getKmlFilename-j2XxQ4]

        return getKmlFilename(createEmptyFolder())
          .catch(e => expect(e).toMatch('No valid KML file in'));
      });

      test('Should throw if no KML files in folder - try/catch version',
        async () => {
        // Expected one assertion to be called but received zero assertion calls.
        // expect.assertions(1);

        try {
          const result = await getKmlFilename(createEmptyFolder());
        } catch (e) {
          // Received value must be a function, but instead "object" was found
          // expect(e).toThrow();

          // expect(string)[.not].toMatch(expected)
          // string value must be a string.
          // Received:
          // object:
          // [Error: No valid KML file in /tmp/test-getKmlFilename-3JOUAX]
          expect(e).toMatch('No valid KML file in');
        }
      });

    });

如您所见，没有任何效果。我相信我的测试几乎完全复制了第一个失败测试的 Promises 示例和最后一个失败测试的 Async/Await 示例，但是没有一个有效。

我相信与 Jest 文档中示例的不同之处在于它们展示了如何测试函数 throws 以​​及如何测试 rejects 的 Promise。但是我的承诺通过抛出来拒绝。

检查节点控制台中的功能我得到了这个日志：

// import function
> getKml = require('./getKmlFileName.js')
[AsyncFunction: getKmlFilename]
// trying it with a proper folder shows we get a Promise
> getKml('/tmp/con')
Promise {
  <pending>,
  domain: 
   Domain {
     domain: null,
     _events: { error: [Function: debugDomainError] },
     _eventsCount: 1,
     _maxListeners: undefined,
     members: [] } }
// trying it with a failing folder shows it's a rejected promise which throws
> getKml('/tmp/sin')
Promise {
  <pending>,
  domain: 
   Domain {
     domain: null,
     _events: { error: [Function: debugDomainError] },
     _eventsCount: 1,
     _maxListeners: undefined,
     members: [] } }
> (node:10711) UnhandledPromiseRejectionWarning: Error: No valid KML file in /tmp/sin
    at getKmlFilename (/home/flc/soft/learning/2018.06.08,jest/getKmlFileName.js:14:11)
    at <anonymous>
    at process._tickDomainCallback (internal/process/next_tick.js:228:7)
(node:10711) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)
(node:10711) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

从内联的 cmets 中可以看出，该函数正在做它应该做的事情，但是我不知道如何在 Jest 中测试它。任何帮助将不胜感激。

如果这里的代码看起来太复杂，我准备了一个repository，其中包含我学习Jest的不幸

2018.06.12 更新：

不知何故，我的信息被打乱了，丢失了第一部分，这是我正在尝试测试的实际代码，对此我深表歉意，这里是：

• getKmlFileName.js

  'use strict';
  const globby = require('globby');
  const path = require('path');
  
  const getKmlFilename = async (workDir) => {
    const pattern = path.join(workDir, '**/*.kml');
    const files = await globby(pattern);
    if (files && files.length > 0) {
      // Return first KML found, if there are others (improbable), ignore them
      return path.basename(files[0]);
    } else {
      throw new Error(`No valid KML file in ${workDir}`);
    }
  };
  
  module.exports = getKmlFilename;
  

Answer 1

在您的第一次测试中：

return getKmlFilename(createEmptyFolder())
  .catch(e => expect(e).toMatch('No valid KML file in'));

如果 Promise 解决，它不会抱怨。

在第二次测试中

try {
  const result = await getKmlFilename(createEmptyFolder());
} catch (e) {
  ...
}

如果 Promise 解决，它也不会抱怨，因为它不会进入 catch 块。

要测试 Promise，请问自己以下问题：

1. 承诺应该成功（解决）还是失败（拒绝）？
2. 您的结果或拒绝值是Error 还是常规对象？

开玩笑，你应该可以这样做：

1. 解析为常规对象：expect(yourThing()).resolves.toMatchSnapshot()
2. 解决错误（从未见过）： expect(yourThing()).resolves.toThrow(/something/)
3. 拒绝错误： expect(yourThing()).rejects.toThrow(/something/)
4. 拒绝常规对象（您确定要这样做吗？）： expect(yourThing()).rejects.toMatchSnapshot()

请注意，异步函数总是返回一个值（一个 Promise 对象），因此“通常的”expect(() => yourThing()).toThrow() 将不起作用。您需要先等待 Promise 的结果（通过使用 resolves 或 rejects）然后进行测试。