Warning in unit tests due to helper class starting with "Test"

[Greg Najda]

============================== warnings summary ===============================
tests/unit_test.py::TestServer
  cannot collect test class 'TestServer' because it has a __init__ constructor

-- Docs: http://doc.pytest.org/en/latest/warnings.html

Could be fixed by renaming the TestServer class to something else.

[denisenkom]

Renamed