I've discovered many
Unprotected by try/catch logic. You can search and find them.
If a test case fails with say, Assert.nyi (such as for encodingErrorPolicy="error") such as test_hexBinary_unparse_14, then the pool is not properly cleaned up, and a subsequent test that just so happens to run on the same thread, then gets an error. E.g., test test_hexBinary_unparse_15 fails with a pool error, as does test_hexBinary_unparse_19. Even though if you run each of these tests individually, it passes.
This creates a situation where tests that should be isolated from each other are in fact interacting with eachother.