Difference between mockClear, mockReset, mockRestore in Jest

Some questions that came up while working on Jest.

Difference between mockClear, mockReset, mockRestore

mockClear clears the call history of a mock.

const mockFn = jest.fn();
mockFn(); // call 1
mockFn(); // call 2
expect(mockFn).toHaveBeenCalledTimes(2);
mockFn.mockClear();
expect(mockFn).toHaveBeenCalledTimes(0);

mockReset clears the call history and removes any mock implementation specified for the mock.

const mockFn = jest.fn(() => 'initial');
mockFn.mockImplementation(() => 'changed');
mockFn(); // returns 'changed'
mockFn.mockReset();
mockFn(); // returns initial

mockRestore removes the mock.

const originalFunction = jest.spyOn(Math, 'abs');
originalFunction.mockImplementation(() => 'mocked');
console.log(originalFunction(-5)); // 'mocked'
originalFunction.mockRestore();
console.log(Math.abs(-5)); // 5

When to use act() in RTL?

Use act() when there are state updates that need to happen after firing an event.

act(() => {
  fireEvent.click(button);
});

Difference between toBeCalled() and toHaveBeenCalled()

toHaveBeenCalled checks if a mock is called at least once. toBeCalled also does the same thing. But it has some variations - toBeCalledWith() that checks the arguments that the mock is called with. The number of times that it is called is also checked in toBeCalledWith assertion.