Jest + TypeScript でテストできるようにする






1️⃣ Jestをinstallする(JavaScriptテスト実行はここまででok👌)

$ npm install --save-dev jest
$ vi package.json //npm testでテスト実行できるようにする
  "devDependencies": {
    "jest": "^27.5.1"
- }
+ },
+ "scripts": {
+   "test": "jest"
+ }

$ npm test //JSのテスト実行できた〜🙌🙌🙌

> test
> jest

 PASS  ./sum.test.js
  ✓ adds 1 + 2 to equal 3 (2 ms)

Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        0.48 s
Ran all test suites.

2️⃣ TypeSciptでもJestでテスト実行できるようにする


$ npm test

> test
> jest

 FAIL  ./ts-sum.test.ts
  ● Test suite failed to run

    Jest encountered an unexpected token

    Jest failed to parse a file. This happens e.g. when your code or its dependencies use non-standard JavaScript syntax, or when Jest is not configured to support such syntax.

    Out of the box Jest supports Babel, which will be used to transform your files into valid JS based on your Babel configuration.

    By default "node_modules" folder is ignored by transformers.

    Here's what you can do:
     • If you are trying to use ECMAScript Modules, see for how to enable it.
     • If you are trying to use TypeScript, see
     • To have some of your "node_modules" files transformed, you can specify a custom "transformIgnorePatterns" in your config.
     • If you need a custom transformation specify a "transform" option in your config.
     • If you simply want to mock your non-JS modules (e.g. binary assets) you can stub them out with the "moduleNameMapper" config option.

    You'll find more details and examples of these config options in the docs:
    For information about custom transformations, see:


    ({"Object.":function(module,exports,require,__dirname,__filename,jest){import { TsSum } from "./ts-sum";

    SyntaxError: Cannot use import statement outside a module

      at Runtime.createScriptFromCode (node_modules/jest-runtime/build/index.js:1728:14)

 PASS  ./sum.test.js

Test Suites: 1 failed, 1 passed, 2 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        1.04 s
Ran all test suites.


$ npm i typescript -g
$ tsc --version
Version 4.6.2

$ tsc -init

Created a new tsconfig.json with:                                                                                       
  target: es2016
  module: commonjs
  strict: true
  esModuleInterop: true
  skipLibCheck: true
  forceConsistentCasingInFileNames: true

You can learn more at
$ npm install --save-dev ts-jest @types/jest typescript
$ jest --init //jest.config.tsを作成

The following questions will help Jest to create a suitable configuration for your project

✔ Would you like to use Typescript for the configuration file? … yes
✔ Choose the test environment that will be used for testing › node
✔ Do you want Jest to add coverage reports? … no
✔ Which provider should be used to instrument code for coverage? › v8
✔ Automatically clear mock calls, instances and results before every test? … no

📝  Configuration file created at /Users/kin29/jest-test/jest.config.ts

$ vi jest.config.ts
- // transform: {}
+ transform: {
+   '.*\\.(ts)$' : '/node_modules/ts-jest',
+ },


$ npm test

> test
> jest

 PASS  ./sum.test.js
 PASS  ./ts-sum.test.ts

Test Suites: 2 passed, 2 total
Tests:       2 passed, 2 total
Snapshots:   0 total
Time:        1.741 s
Ran all test suites.