# my_module.py
def greet(name):
    return f"Hello, {name}!"

# test_my_module.py
def test_greet(mocker):
    mock_greet = mocker.patch('my_module.greet', return_value="Hi!")
    assert mock_greet("Alice") == "Hi!"
    mock_greet.assert_called_once_with("Alice")