- move testplugin and its related files into their own `tests/plugin`
directory, so that tests don't have to unnecessarily import regular
plugin test files
- refactor test_session
- don't initialize session in `setUp`
- add test cases for ImportError and SyntaxError
- add assertion for plugin override debug log call
- rename "load_plugins" test cases
- rename some confusing variable names
- fix remaining tests in regards to the testplugin path changes
bastimeyer