preset: ts-jest とは

npm i -D jest @types/jest typescript

npx jest --init

npx tsc --init

export const sum = (left: number, right: number): number => {
  return left + right
}

console.log(sum(1, 2))

import { sum } from "."

describe("index.js", () => {
  it("should be 3 when inputs are 1, 2", () => {
    const actual = sum(1, 2)
    expect(actual).toBe(3)
  })
})

module.exports = {
  clearMocks: true,
  // Indicates which provider should be used to instrument code for coverage
  coverageProvider: "babel",
  // A preset that is used as a base for Jest's configuration
  // preset: undefined,
  // The test environment that will be used for testing
  testEnvironment: "node",
  // A map from regular expressions to paths to transformers
  // transform: undefined,
}

{
  "compilerOptions": {
    "target": "es5",
    "module": "commonjs",
    "outDir": "./dist",
    "strict": true,
    "esModuleInterop": true,
    "skipLibCheck": true,
    "forceConsistentCasingInFileNames": true
  },
  "include": ["src"]
}

npm run test

 FAIL  src/index.test.ts
  ● Test suite failed to run

    Jest encountered an unexpected token

    This usually means that you are trying to import
    a file which Jest cannot parse, e.g. it's not plain JavaScript.

    By default, if Jest sees a Babel config,
    it will use that to transform your files, ignoring "node_modules".

    Here's what you can do:
     • 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:
    https://jestjs.io/docs/en/configuration.html

    Details:

    import { sum } from ".";
    ^^^^^^

    SyntaxError: Cannot use import statement outside a module

      at Runtime._execModule

Test Suites: 1 failed, 1 total
Tests:       0 total
Snapshots:   0 total
Time:        1.13 s
Ran all test suites.

npm i -D ts-jest

module.exports = {
  clearMocks: true,
  // Indicates which provider should be used to instrument code for coverage
  coverageProvider: "babel",
  // A preset that is used as a base for Jest's configuration
  preset: "ts-jest",
  // The test environment that will be used for testing
  testEnvironment: "node",
  // A map from regular expressions to paths to transformers
  // transform: undefined,
}

$ npm run test

 PASS  src/index.test.ts
  index.js
    ✓ should be 3 when inputs are 1, 2 (2 ms)

  console.log
    3

      at Object.<anonymous> (src/index.ts:5:9)

Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        3.041 s
Ran all test suites.

module.exports = {
  clearMocks: true,
  coverageProvider: "babel",
  preset: undefined,
  testEnvironment: "node",
  transform: {
    ".ts": "ts-jest",
  },
}

export function createJestPreset(
  { allowJs = false }: CreateJestPresetOptions = {},
  from: Config.InitialOptions = {}
): TsJestPresets {
  logger.debug(
    { allowJs },
    "creating jest presets",
    allowJs ? "handling" : "not handling",
    "JavaScript files"
  )

  return {
    transform: {
      ...from.transform,
      [allowJs ? "^.+\\.[tj]sx?$" : "^.+\\.tsx?$"]: "ts-jest",
    },
    ...(from.testMatch ? { testMatch: from.testMatch } : undefined),
    ...(from.moduleFileExtensions
      ? { moduleFileExtensions: from.moduleFileExtensions }
      : undefined),
  }
}