Jest Testing Framework

Setting up Jest

npm i jest --save-dev

Next, create a test script in package.json. The script itself is jest. This allows you to use npm test to run the Jest test suite.

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"scripts": {
    "start": "node src/index.js",
    "dev": "env-cmd -f ./config/dev.env nodemon src/index.js",
    "test": "jest"
  },

Now, you’ll need to create a test suite. This is a file in your project that ends with .test.js. The file extension allows Jest to find and run the test suites for your project.

Creating a Test Case

You can add a test case to a test suite using the test function. Jest provides various functions as global variables in your test suite files. test is one of them. The first argument to test is the name of your test case. The second argument to test is the test function itself.

If the test function throws an error, the test cast will fail. If the test function doesn’t throw an error, the test case will pass.

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test('Hello World', ()=>{

})

test('This should fail', ()=>{
  throw new Error("Failure!")
})

Ref : The Complete Node.js Dev Course by Andrew Mead