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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.
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const cal = require('../index');
test('adds 1 + 2 to equal 3', () => {
expect(cal.sum(1, 2)).toBe(3);
expect(cal.sum(1, 2)).not.toBe(4);
expect(cal.sum(1, 2)).toBeGreaterThan(2);
expect(cal.sum(1, 2)).toBeLessThan(4);
expect(cal.sum(1, 2)).toBeCloseTo(3);
// Testing datatype
expect(typeof cal.sum(1, 2)).toBe("number");
});