Minimum version requirements for sanity tests have been standardized:
- All single version sanity tests now require Python 3.5 or later.
- All multiple version sanity tests continue to use all supported Python versions.
- All version neutral sanity tests continue to work on any supported Python version.
Previously some tests required 3.5 or later with most of the remaining tests requiring 2.7 or later.
When using the `--python` option to specify a Python version:
- Tests which do not support the specified Python version will be skipped with a warning.
- If the specified Python version is not available, any test attempting to use it will generate an error.
When not using the `--python` option to specify a Python version:
- Multiple version tests will attempt to run on all supported versions.
- Single version tests will use the current version if supported and available, or if no supported version is available.
- Single version tests will use the lowest available and supported version if the current version is not supported.
- Any versions which are not available or supported will be skipped with a warning.
Unit tests automatically skip unavailable Python versions unless `--python` was used to specify a version.
* Move sanity into directory.
* Omit abstract classes from returned subclass list.
* Split sanity tests out into plugins.
* Fix abstract class handling for Python 3.
