Added valid test to professor. Checking for presence of first name
Moved test for presence of first name to test on @ user because it is not specific to Assistant or Professor
Added tests for presence of last name and email
Added tests for length of first and last name
Added test for length of email and moved responds to statements above the actual tests. Also moved the let statements to the top so they would be completed before running any tests
Added test for presence of password
Added test for presence of password confirmation and password/password_confirmation mismatch is caught
Added test for minimum length of password
Added test for email formatting