Log Message:
py-test: updated to 4.2.1

pytest 4.2.1:

Bug Fixes
- The pytest_report_collectionfinish hook now is also called with --collect-only.
- Do not raise UsageError when an imported package has a pytest_plugins.py child \ 
module.
- Fix output capturing when using pdb++ with recursive debugging.
- Fix handling of collect_ignore via parent conftest.py.
- Fix regression where setUpClass would always be called in subclasses even if \ 
all tests
  were skipped by a unittest.skip() decorator applied in the subclass.
- Fix parametrize(... ids=<function>) when the function returns non-strings.
- Fix/improve collection of args when passing in __init__.py and a test file.
- more_itertools is now constrained to <6.0.0 when required for Python 2.7 \ 
compatibility.
- Fix "ValueError: Plugin already registered" exceptions when running \ 
in build directories that symlink to actual source.

Improved Documentation
- Add note to plugins.rst that pytest_plugins should not be used as a name for a \ 
user module containing plugins.
- Document how to use raises and does_not_raise to write parametrized tests with \ 
conditional raises.
- Document how to customize test failure messages when using
  pytest.warns.

Trivial/Internal Changes
- Some verbosity related attributes of the TerminalReporter plugin are now
  read only properties.