AstroのユニットテストをJestで行う【ESモジュール対処法】

pnpm add --save-dev typescript jest ts-jest @types/jest

pnpm ts-jest config:init

export function writeLog(log: string) {
  return console.log(log)
}

import { writeLog } from '../src/utils/sample'

test('最初のテスト', () => {
  writeLog('OK')
})

$ pnpm jest
 FAIL  test/initial.test.ts
  ● Test suite failed to run

    test/initial.test.ts:1:10 - error TS1286: ESM syntax is not allowed in a CommonJS module when 'verbatimModuleSyntax' is enabled.

    1 import { writeLog } from '../src/utils/sample'
               ~~~~~~~~

Test Suites: 1 failed, 1 total
Tests:       0 total
Snapshots:   0 total
Time:        2.513 s
Ran all test suites.

{
  "compilerOptions": {
    "target": "es2021",
    "module": "commonjs",
    "esModuleInterop": true,
    "forceConsistentCasingInFileNames": true,
    "strict": true,
    "skipLibCheck": true
  }
}

/* prettier-ignore */
/** @type {import('ts-jest').JestConfigWithTsJest} */
export default {
  preset: 'ts-jest', 
  preset: 'ts-jest/presets/default-esm', 
  testEnvironment: 'node',
  transform: { 
    '^.+\\.ts?$': [ 
      'ts-jest', 
      { 
        useESM: true, 
        tsconfig: 'tsconfig.test.json'
      } 
    ] 
  } 
}

$ pnpm jest
  console.log
    OK

      at writeLog (src/utils/sample.ts:2:17)

 PASS  test/initial.test.ts
  ✓ 最初のテスト (14 ms)

Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        1.792 s
Ran all test suites.

{
  "jest.jestCommandLine": "pnpm jest"
}