How do you unit test regular expressions?

Question

I\'m new to TDD, and I find RegExp quite a particular case. Is there any special way to unit test them, or may I just treat them as regular functions?

Answer 1

Presumably your regular expressions are contained within a method of a class. For example:

public bool ValidateEmailAddress( string emailAddr )
{
    // Validate the email address using regular expression.
    return RegExProvider.Match( this.ValidEmailRegEx, emailAddr );
}

You can now write tests for this method. I guess the point is is that the regex is an implementation detail - your test needs to test the interface, which in this case is just the validate email method.