Mock Implementation

Mock Implementation

In this section, we will discuss two ways of mock implementation.

1. Mock a function with jest.fn
   This is the most basic way of mocking in which the original function is reassigned to a mock function. Then the mock function will be called at all the places of the reassigned function.
   “jest.fn(implementation)” or “jest.fn().mockImplementation(implementation)” accepts a function and uses it as the mock implementation.
    
2. Mock a function with jest.spyOn
   The method jest.spyOn can be used to mock either the whole module or its individual functions. It is used in the cases where we need to spy on a method but keep the original implementation and in the cases where we need to mock the implementation but restore the original.
   “jest.spyOn(object, methodName)” creates a mock function as jest.fn but also tracks calls to object[methodName].

FAQs-

1. When to use Mock Functions?

 Ans: We can use Mock Functions in two conditions. First, when we want to replace the      return value for a specific function. Second, when we want to check if our test subject is executing a function in a certain way

Key takeaways-

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