Is.StringMatching() takes a string argument, which is to be used as a regular expression. Hence, it must be a valid regular expression. You should either use Is.EqualTo() or escape the ')' like this: @"NUnit is :\) happy!"
Is.StringMatching() takes a string argument, which is to be used as a regular expression. Hence, it must be a valid regular expression. You should either use Is.EqualTo() or escape the ')' like this: @"NUnit is :\) happy!"