tests: fix traceback for integration tests

Summary: Set `__unittest = True` in testcase.py so stack frames from testcase.py are skipped by default. This fixes test output not showing the actual test assertion that failed.

Reviewed By: vilatto

Differential Revision: D90263225

fbshipit-source-id: 4889a826bc3c381867a2aea84a2e6e1e17351e9e

Author: muirdm

eden/test_support/testcase.py

@@ -17,6 +17,10 @@
 from . import environment_variable as env_module
 from .temporary_directory import TempFileManager
 
+# Tell Python's unittest traceback handling to hide frames from this module
+# so test failures show the actual test code, not our wrapper methods.
+__unittest = True
+
 
 def _is_forkpty_deprecation_warning(w: warnings.WarningMessage) -> bool:
     """Check if a warning is the forkpty deprecation warning from pty.py.