Fix ArgvContext to isolate logging configuration

Co-authored-by: bittner <[email protected]>

Author: Copilot

cli_test_helpers/decorators.py

@@ -3,6 +3,7 @@
 """
 
 import contextlib
+import logging
 import os
 import sys
 from tempfile import TemporaryDirectory
@@ -18,17 +19,27 @@ class ArgvContext:
     Use it to mimic the command line arguments of the CLI application.
     Note that the first argument (index ``0``) is always the script or
     application name.
+
+    This context manager also isolates logging configuration by temporarily
+    clearing logging handlers when entering the context and restoring them
+    when exiting. This allows code under test to call ``logging.basicConfig()``
+    successfully even when test frameworks (like pytest) have already
+    configured logging handlers.
     """
 
     def __init__(self, *new_args):
         self._old = sys.argv
         self.args = type(self._old)(new_args)
+        self._old_handlers = None
 
     def __enter__(self):
         sys.argv = self.args
+        self._old_handlers = logging.root.handlers[:]
+        logging.root.handlers.clear()
 
     def __exit__(self, exc_type, exc_val, exc_tb):
         sys.argv = self._old
+        logging.root.handlers = self._old_handlers
 
 
 class EnvironContext(patch.dict):

cli_test_logging.py

@@ -1,7 +1,10 @@
 """Tests for our tests helpers.  8-}."""
 
+import logging
 import os
 import sys
+import tempfile
+from pathlib import Path
 
 from cli_test_helpers import ArgvContext, EnvironContext, RandomDirectoryContext
 
@@ -23,6 +26,61 @@ def test_argv_context():
     assert sys.argv == old, "sys.argv wasn't correctly reset"
 
 
+def test_argv_context_logging_isolation():
+    """
+    Does ArgvContext isolate logging configuration?
+
+    This test verifies that ArgvContext temporarily clears logging handlers,
+    allowing code under test to call logging.basicConfig() successfully even
+    when test frameworks have already configured logging.
+    """
+    # Setup: Create a mock handler to simulate pytest's handlers
+    original_handlers = logging.root.handlers[:]
+    mock_handler = logging.NullHandler()
+    logging.root.handlers.append(mock_handler)
+
+    try:
+        # Verify the mock handler is present
+        assert mock_handler in logging.root.handlers, "Test setup failed"
+
+        with tempfile.TemporaryDirectory() as tmpdir:
+            logfile = Path(tmpdir) / "test.log"
+
+            with ArgvContext("test_script.py", str(logfile)):
+                # Inside context: handlers should be cleared
+                handlers_before = logging.root.handlers[:]
+                assert len(handlers_before) == 0, (
+                    "Handlers should be cleared inside ArgvContext"
+                )
+
+                # Configure logging (this should work now)
+                logging.basicConfig(
+                    filename=str(logfile),
+                    level=logging.INFO,
+                    force=False,  # Should work without force since handlers are cleared
+                )
+
+                # Log a message
+                logger = logging.getLogger(__name__)
+                logger.info("Test message")
+
+            # After context: handlers should be restored
+            assert mock_handler in logging.root.handlers, (
+                "Original handlers should be restored after ArgvContext"
+            )
+
+            # Verify the log file was created and contains the message
+            assert logfile.exists(), "Log file should have been created"
+            log_content = logfile.read_text()
+            assert "Test message" in log_content, (
+                "Log file should contain the test message"
+            )
+
+    finally:
+        # Cleanup: Restore original handlers
+        logging.root.handlers = original_handlers
+
+
 def test_environ_context():
     """
     Does EnvironContext set new environ values and reset old ones correctly?