Give a simple example of Jest test case

Let's write a test for a function that adds two numbers in sum.js file:

const sum = (a, b) => a + b;

export default sum;

Create a file named sum.test.js which contains actual test:

import sum from "./sum";

test("adds 1 + 2 to equal 3", () => {
expect(sum(1, 2)).toBe(3);
});

And then add the following section to your package.json:

{
"scripts": {
  "test": "jest"
}
}

Finally, run yarn test or npm test and Jest will print a result:

$ yarn test
PASS ./sum.test.js
✓ adds 1 + 2 to equal 3 (2ms)

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