gh-gpshead-cpython-skills-plugins-cpython-skills/skills/cpython-testing/SKILL.md

name, description

name	description
cpython-testing	Use this skill when you need to run CPython tests, whether running individual test files, specific test cases, the full test suite, or collecting code coverage. It covers unittest-based testing (not pytest), debugging tests, and test best practices.

Running CPython Tests

Critical rules:

1. ALWAYS use sub-agents when running tests
2. NEVER use pytest - CPython tests are unittest based
3. Use --match not -k for filtering (this is not pytest!)

Prerequisite: BUILT_PY=build/python or build/python.exe

Running Tests

# Single test module (recommended - proper discovery, parallel execution)
$BUILT_PY -m test test_zipfile -j $(nproc)

# Multiple modules
$BUILT_PY -m test test_csv test_json -j $(nproc)

# Direct execution (quick but may miss test packages)
$BUILT_PY Lib/test/test_csv.py

# Specific test pattern (use --match, NOT -k!)
$BUILT_PY -m test test_zipfile --match "*large*" -j $(nproc)
$BUILT_PY -m test test_csv --match "TestDialect*"
$BUILT_PY -m test test_json --match "TestEncode.test_encode_string"

# Full test suite (ASK FIRST - takes significant time!)
make -C $BUILD_DIR test

# Useful flags: -v (verbose), -f (fail fast), --list-tests (show all), --help

Test packages (directories like test_asyncio/) require load_tests() in __init__.py to work with python -m test.

Code Coverage

# Collect coverage (uses trace mechanism via libregrtest)
$BUILT_PY -m test --coverage test_csv test_json --coveragedir .claude/coverage/ -j $(nproc)

# Reports go to specified coveragedir

Debugging

For interactive debugging (pdb/lldb/gdb) or testing REPL features: Control a tmux session.

Add breakpoint() in test code, then run with -v for verbose output.