So if we want to mock the useRouter hook in NextJs, we can use vi for it. The "vi" library's function vi.mock allows us to simulate the behaviour of the useRouter hook. The mock function returns an object that mimics the Router object's properties and methods.

vi.mock("next/router", () => ({
    useRouter: () => ({
      replace: vi.fn(),
    }),
  }));

replace: a mock function that simulates the behavior of the replace method of the Router object. If we do not use it, the test might fail and we get the following error. Error: NextRouter was not mounted.