Production code must not detect test runs

Flags code outside test files that checks whether it is running under test:

• JS/TS: process.env.NODE_ENV === 'test' (or !==), process.env.JEST_WORKER_ID, process.env.VITEST, import.meta.env.VITEST, typeof jest !== 'undefined'
• Python: 'pytest' in sys.modules, PYTEST_CURRENT_TEST
• Go: testing.Testing(), flag.Lookup("test.v"), a .test suffix check on os.Args[0]

Test files, conftest.py, setupTests* and *.config.* files are not scanned. Commented-out lines are ignored.

Why it matters with coding agents: making the code take a different path under test is a way to turn a failing test green without fixing the code it tests.

WARN only: nothing is blocked. The frame sees the files as pushed, so it reports every case present, not only new ones.

Fix#

Make the code correct in both cases and inject the difference from the test (a parameter, a fake, a config value). If a branch is intended (quieter logging under test), record why: a whitelist entry with a reason, or appframes:disable-next-line app-correctness/no-test-special-casing in a comment above it.