write jest tests code example

Example 1: testing with jest

npm i jest --save -dev
-> In Package.json change the Script object(watchAll - jest will run auto)
"test" : "jest --watchAll"
-> test file should be named such way that re used by jest can recognize it
like filename.<test> or <spec> or skip it.js
Ex: sum.test.js or sum.spec.js or sum.js
-> require the target for testing file in this test file then enjoy testing.
-> visit jestWebsite-> Docs.

Example 2: jest

const sum = require('./sum');

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