JestでTypeScriptのテストを書く(Step3:API検証)

はじめに

表題通り、JestでTypeScriptのテストを書きます。
下記StepでJestの学習を進めていきます

Step1: Jest(環境構築から実行まで)
Step2: Jest(Matcherを利用する)
Step3: Jest(API検証)←今回はここ
Step4: Jest(StubとMockとSpy)

API通信

ディレクトリ構成

~/develop/react/jest_ts$ tree -I node_modules 
.
├── jest.config.js
├── package.json
├── src
│   ├── __tests__
│   │   ├── api.test.ts
│   │   ├── sample.test.ts
│   │   └── sum.test.ts
│   ├── api.ts
│   └── sum.ts
├── tsconfig.json
└── yarn.lock

3 directories, 9 files

src/api.ts

import axios from 'axios';

export const fetchData = async (url) => {
  try {
    const response = await axios.get(url);
    return response.data;
  } catch (error) {
    throw error;
  }
};

src/__tests__/api.test.ts

import axios from 'axios';
import { fetchData } from '@/api';

// axios.get を手動でモックに設定
axios.get = jest.fn();

describe('fetchData', () => {
  it('fetches successfully data from an API', async () => {
    // mockを準備
    const data = { data: 'some data' };
    (axios.get as jest.Mock).mockResolvedValue({ data });

    await expect(fetchData('https://example.com')).resolves.toEqual(data);
  });

  it('fetches erroneously data from an API', async () => {
    // mockを準備
    const errorMessage = 'Network Error';
    (axios.get as jest.Mock).mockRejectedValue(new Error(errorMessage));

    await expect(fetchData('https://example.com')).rejects.toThrow(
      errorMessage
    );
  });
});

実行結果

テスト実行

~/develop/react/jest_ts$ yarn test api.test.ts 
yarn run v1.22.19
$ jest api.test.ts
ts-jest[config] (WARN) message TS151001: If you have issues related to imports, you should consider setting `esModuleInterop` to `true` in your TypeScript configuration file (usually `tsconfig.json`). See https://blogs.msdn.microsoft.com/typescript/2018/01/31/announcing-typescript-2-7/#easier-ecmascript-module-interoperability for more information.
 PASS  src/__tests__/api.test.ts
  fetchData
    ✓ fetches successfully data from an API (2 ms)
    ✓ fetches erroneously data from an API (2 ms)

Test Suites: 1 passed, 1 total
Tests:       2 passed, 2 total
Snapshots:   0 total
Time:        0.599 s, estimated 1 s
Ran all test suites matching /api.test.ts/i.
✨  Done in 1.15s.