fake-driven-testing

This skill should be used when writing tests, fixing bugs, adding features, or modifying the gateway layer. Use when you need guidance on testing architecture, working with fakes, implementing ABC gateway interfaces, or understanding the defense-in-depth testing strategy. Essential for maintaining test quality and understanding where different types of tests belong.

Refactor tests that use unittest.mock.patch or MagicMock into erk's gateway-based fake pattern. Use when tests import unittest.mock, use @patch decorators, or directly call mock.patch() as context managers. Essential when test_*.py files patch module-level attributes like subprocess.run, shutil.which, os.environ, or other system calls. Covers both making source code injectable AND rewriting tests.