Exclude invalid exceptions from filterwarnings

Ref #355

cheroot/test/_pytest_plugin.py

@@ -0,0 +1,29 @@
+"""Local pytest plugin.
+
+Contains hooks, which are tightly bound to the Cheroot framework
+itself, useless for end-users' app testing.
+"""
+
+from __future__ import absolute_import, division, print_function
+__metaclass__ = type
+
+from pytest import __version__
+
+
+pytest_version = tuple(map(int, __version__.split('.')))
+unraisable_exceptions = {
+    ('pytest', 'PytestUnhandledThreadExceptionWarning'),
+    ('pytest', 'PytestUnraisableExceptionWarning'),
+}
+
+
+def pytest_load_initial_conftests(early_config, parser, args):
+    """Drop unfilterable warning ignores."""
+    if pytest_version >= (6, 2, 0):
+        return
+
+    early_config._inicache['filterwarnings'] = [
+        fw for fw in early_config.getini('filterwarnings')
+        if fw.count(':') < 2 or
+        tuple(fw.split(':')[2].split('.')[:2]) not in unraisable_exceptions
+    ]

pytest.ini

@@ -26,6 +26,9 @@ addopts =
     --cov-report term-missing:skip-covered
     --cov-report xml
     # --cov-report xml:.test-results/pytest/cov.xml  # alternatively move it here
+
+    # pre-load an in-tree plugin
+    -p cheroot.test._pytest_plugin
 doctest_optionflags = ALLOW_UNICODE ELLIPSIS
 filterwarnings =
     error