/// Trait representing a Mocker.
/// A Mocker is a little utility which has a method which determines if the current letter should be uppercase or not.
/// Function that performs the mocking. It takes in a string type and a mocker by reference.
/// It will return a String with the mocking performed.
/// # Examples
///
/// ```
/// let data = String::from("hello world");
/// let result = mock(&data, &AlternatingMocker::new());
///
/// assert_eq!(String::from("hElLo wOrLd"), result);
/// ```