Which Is Jest Way For Restoring Mocked Function

Mocking functions is a common practice in software development, especially when testing code. It allows you to simulate the behavior of certain functions or methods so that you can control their output and focus on testing specific parts of your code. However, there may come a time when you need to restore a mocked function back to its original implementation. But which is the best way to do this? In this article, we'll explore different methods for restoring mocked functions using Jest, a popular testing framework for JavaScript.

One of the simplest methods for restoring a mocked function in Jest is to use the jest.spyOn() method. This method allows you to mock a function and spy on its calls without affecting its original implementation. To restore the mocked function, you can simply call the mockRestore() method on the mocked function. This will revert the function to its original behavior and implementation.

Here's an example demonstrating how to use jest.spyOn() and mockRestore() to restore a mocked function:

// Original function
function add(a, b) {
  return a + b;
}

// Mocking the function
const mockedAdd = jest.spyOn(global, 'add').mockImplementation(() => 10);

console.log(add(2, 3)); // Output: 10

// Restoring the mocked function
mockedAdd.mockRestore();

console.log(add(2, 3)); // Output: 5 (original behavior)

Another approach for restoring a mocked function is to use the jest.restoreAllMocks() method. This method is helpful when you have multiple mocked functions that need to be restored simultaneously. jest.restoreAllMocks() restores all mocked functions created using jest.spyOn() or jest.fn() to their original implementations.

Here's an example demonstrating how to use jest.restoreAllMocks() to restore multiple mocked functions:

// Mocking functions
const mockedFunc1 = jest.spyOn(global, 'func1').mockReturnValue('mockedResult1');
const mockedFunc2 = jest.spyOn(global, 'func2').mockReturnValue('mockedResult2');

// Restoring all mocked functions
jest.restoreAllMocks();

// Now both mocked functions are restored to their original implementations

It's important to note that restoring mocked functions is crucial to ensure that your tests are reliable and accurately reflect the behavior of your code. Failing to restore mocked functions can lead to unexpected behavior and false positives or negatives in your test results.

In conclusion, while there are multiple ways to restore mocked functions in Jest, using jest.spyOn() with mockRestore() or jest.restoreAllMocks() are two commonly used methods. By understanding these approaches and incorporating them into your testing practices, you can maintain the integrity of your tests and ensure that your code behaves as expected both during development and after deployment.