tests/tools/test_local_env_blocklist.py::TestPythonpathSelectiveStrip::
test_execute_code_composition_strips_inherited_hermes_entries hands code_kernel a MagicMock
process whose stdout/stderr only fake read(); the kernel drains with read1(), which on a bare
MagicMock never returns EOF. _stdout_reader died on `buf += chunk`, but _stderr_reader's
`while chunk := stderr.read1(4096)` spun forever appending mocks (each call growing
mock_calls) in a daemon thread that outlived the test: ~1 GB/min until the kernel killed the
worker. Five OOM incidents on this file (08-30, 09-13, 09-14, 09-16, 09-19), always blamed on
whichever test ran next. The fake now returns EOF from read1() as well.
Runner guardrails so the next runaway is a traceback, not a swap storm:
- each pytest worker runs under RLIMIT_DATA (8 GiB, Linux; HERMES_TEST_WORKER_MEM_GB, 0 = off).
RLIMIT_AS is avoided on purpose: browsers spawned by tests reserve huge address space.
- a worker killed by signal or the file timeout is never --file-retries relaunched; a runaway
relaunched while the first tree is still being reaped doubled the damage on 09-16.
Live: the file went from 20 min / 20 GB to 5.6 s / 140 MB. An allocate-forever probe dies with
MemoryError in 5 s; a SIGKILL'd worker launches once on this runner, twice on base.
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