The PTVS python Test Adaptor only discovers tests that have a method which starts with "test_" instead of just "test" which is what is defined in the standard.
"A testcase is created by subclassing unittest.TestCase. The three individual tests are defined with methods whose names start with the letters test. This naming convention informs the test runner about which methods represent tests."
Python Docs Reference
Please remove the underscore requirement.
Note: I'm currently reviewing PTVS 2.0 RC for VS2012 SP3 with Python 3.2 and looking into the Test Explorer integration with the new test adapter in this PTVS release (when compared with PTVS v1.5).