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$ curl repovive.com/roadmaps/javascript/testing-javascript/spies

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$ curl repovive.com/roadmaps/javascript/testing-javascript/spies

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Spies - Testing JavaScript | JavaScript | Repovive

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JavaScript22 sections · 783 units18h total

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Spies

Watch real function calls

Spies watch real functions without replacing them:

const spy = jest.spyOn(console, 'log');

myFunction(); // calls console.log internally

expect(spy).toHaveBeenCalled();
expect(spy).toHaveBeenCalledWith('expected message');

spy.mockRestore(); // Restore original

Spies are useful when you want to verify calls but keep real behavior.