I have some testing methods that are no longer needed, can there be some reason to keep these tests and mark them as deprecated (if so, use the "deprecated" method attribute) to do this)? Or will I just delete them?
Assuming you are using MsTest, you have several options.
If you are really sure that you will no longer need it, I will delete it.
-, . , , , . grokking .
, , - .
, . , , (System Under Test). , .
, unittesting . nunit IgnoreAttribute, .