Added more unit tests to ValidUrlParserTests to up coverage to 95%

[stho32]

Hello dear HMol,

i got to your project using up-for-grabs which saw a few issues one could help with.

I wrote a few unit tests for you to up your coverage on the ValidUrlParser from 86 to 95%.
I can't get to 100% coverage because I could not think of an url that passes the RegEx and Uri.TryCreate test and still fails at the other two tests for / and //.

Please feel free to review my work and tell me everything that I may correct.
I'd like to use that feedback then to push your coverage a little further, in a way that is benefitial to you.
E.g. I recognized that the way I name tests is different from yours. Is that ok for you? If not, what naming convention would you like me to use?

Thank you for your work and time,
stho32