Add the text below into package.json for npm test to run test.

 "scripts": {
        "test": "vitest",
        "test:ui": "vitest --ui",
        "test:run": "vitest run"
    },

Run npm install -D vitest to install vitest in your folder or workspace Run tsc --init to create tsconfig.json file Run npm test and change a test or source code to see HMR in action!