Use {[testenv]deps}, instead of repeating testing requirements. Write another failing test for #109
Revert "Fixed issue in test_nested_context_managers_with_session_created_before_first_nesting. by using a single class and patching cassette on that class. Not a great solution :\"

This reverts commit 2bf23b2cdf8542f5bf137e386f3bc278bbc2cc83.
Fix some of the issues from #109
Mark bad test xfail.