Jest Mocking Patterns

Master Jest mocking techniques to isolate code under test from external dependencies.

Basic Mocking with jest.fn()

Creating Mock Functions

// Simple mock function
const mockFn = jest.fn();
mockFn('arg1', 'arg2');

expect(mockFn).toHaveBeenCalled();
expect(mockFn).toHaveBeenCalledWith('arg1', 'arg2');
expect(mockFn).toHaveBeenCalledTimes(1);

// Mock with return value
const mockWithReturn = jest.fn().mockReturnValue(42);