Merge pull request #41 from gsalgado/vp

Get rid of redundant tests for create/replace series
Lowercased error messages, cleared up comments, shortened some lines.
No functional changes.
Merge pull request #43 from teknico/vp

Lowercased error messages, cleared up comments, shortened some lines.
New test helper function to check that we got the error we wanted

This simplifies a bunch of our tests and, again, reduces duplication