C:\practice-ts>node --version
v22.19.0
C:\practice-ts>npm --version
10.8.2

PS C:\ts-practice> npm init -y
Wrote to C:\works-ts\package.json:

{
...
  "author": "<YOUR NAME>", # 본인 이름으로 수정
  "license": "MIT", # MIT 라이선스로 수정
...
}

function sum(a, b) {
    return a + b;
}

console.log(sum(1, 2));
console.log(sum("Hello", [0, 1, 2]));

$ node src\sum.js
3
Hello0,1,2

PS C:\ts-practice> npm install -D typescript jest ts-node ts-jest @types/jest @types/node

npm warn deprecated inflight@1.0.6: This module is not supported, and leaks memory. Do not use it. Check out lru-cache if you want a good and tested way to coalesce async requests by a key value, which is much more comprehensive and powerful.
npm warn deprecated glob@7.2.3: Glob versions prior to v9 are no longer supported

added 324 packages, and audited 325 packages in 15s

44 packages are looking for funding
  run `npm fund` for details

found 0 vulnerabilities

PS C:\ts-practice> npx tsc --init

Created a new tsconfig.json

PS C:\ts-practice> npx ts-jest config:init    

Jest configuration written to "C:\works-ts\jest.config.js".

import { sum } from 'sum';

describe('sum 함수 테스트', () => {
  test('두 숫자를 더하면 올바른 결과를 반환한다', () => {
    expect(sum(2, 3)).toBe(5);
    expect(sum(-5, 10)).toBe(5);
    expect(sum(-2, -3)).toBe(-5);
    expect(sum(0, 5)).toBe(5);
    expect(sum(1.5, 2.3)).toBeCloseTo(3.8);
    expect(sum(1000000, 2000000)).toBe(3000000);
    expect(sum(Number.MAX_SAFE_INTEGER, -1)).toBe(Number.MAX_SAFE_INTEGER - 1);
  });
});

...
"type": "module",
"scripts": {
    "test": "jest",
    "test:watch": "jest --watch",
    "test:coverage": "jest --coverage"
},
...

export function sum(x, y) {
    return x + y;
}

{
  "compilerOptions": {
    "rootDir": "./src",
    "outDir": "./dist",
    "module": "nodenext",
    "target": "esnext",
    // "lib": ["esnext"],
    "types": ["node", "jest"],
    // Other Outputs
    "sourceMap": true,
    "declaration": true,
    "declarationMap": true,
    // Stricter Typechecking Options
    "noUncheckedIndexedAccess": true,
    "exactOptionalPropertyTypes": true,
    // Style Options
    // "noImplicitReturns": true,
    // "noImplicitOverride": true,
    // "noUnusedLocals": true,
    // "noUnusedParameters": true,
    // "noFallthroughCasesInSwitch": true,
    // "noPropertyAccessFromIndexSignature": true,
    // Recommended Options
    "strict": true,
    "jsx": "react-jsx",
    "verbatimModuleSyntax": false,
    "isolatedModules": true,
    "noUncheckedSideEffectImports": true,
    "moduleDetection": "force",
    "skipLibCheck": true,
    "esModuleInterop": true,
    "allowSyntheticDefaultImports": true,
    "baseUrl": ".",
    "paths": {
      "@/*": [
        "src/*"
      ]
    }
  }
}

import { createDefaultPreset } from "ts-jest";

const tsJestTransformCfg = createDefaultPreset().transform;

export default {
  preset: "ts-jest",
  testEnvironment: "node",
  roots: ["<rootDir>/src"],
  testMatch: ["**/__tests__/**/*.ts", "**/?(*.)+(spec|test).ts"],
  collectCoverageFrom: ["src/**/*.ts", "!src/**/*.d.ts"],
  transform: {
    '^.+\\.ts$': ['ts-jest', {
      useESM: true,
      tsconfig: {
        module: 'esnext',
        target: 'esnext',
        moduleResolution: 'node',
        verbatimModuleSyntax: false
      }
    }]
  },
  moduleNameMapper: {
    '^@/(.*)$': '<rootDir>/src/$1'
  },
  extensionsToTreatAsEsm: ['.ts']
};

import { sum } from '@/sum';

PS C:\ts-practice> npm run test

> temp_a@1.0.0 test
> jest

 PASS  src/__tests__/sum.test.ts
  sum 함수 테스트
    √ 두 숫자를 더하면 올바른 결과를 반환한다 (2 ms)                                                                                                                    
                                                                                                                                                                        
Test Suites: 1 passed, 1 total                                                                                                                                          
Tests:       1 passed, 1 total                                                                                                                                          
Snapshots:   0 total
Time:        0.352 s
Ran all test suites.