What is the difference between jest.mock and jest.spyOn?

What is the difference between jest.mock and jest.spyOn?

jest.mock is used to mock entire modules, while jest.spyOn is used to spy on specific methods of an object.

Can you give me an example of how to use jest.spyOn?

Sure! You can use it like this: const mySpy = jest.spyOn(object, 'method'); to track calls to 'method'.

When should I use jest.mock instead of jest.spyOn?

Use jest.mock when you want to replace the entire module's implementation, and jest.spyOn when you want to keep the original implementation but track calls.

Are there any performance implications of using these methods?

Yes, using jest.mock can lead to slower tests if the mocked module is large, while jest.spyOn is generally lighter since it only tracks method calls.