Test Isolation Contract

Tests never read or write the real ~/.hermes. This is enforced, not just convention.

The `isolate_hermes_home` fixture

An autouse pytest fixture in conftest.py redirects HERMES_HOME to a fresh per-test temp directory. HOME and USERPROFILE are also pinned to the same temp dir as a safety net for any Path.home() fallback.

The poison-file test (`test_isolation.py`)

test_isolation.py plants a poisoned sentinel file in a decoy home directory and asserts that no code path reads it. This is a fail-closed check: any new code that reaches outside HERMES_HOME will break this test before it breaks production data.

Rule for new code: always locate Hermes files via os.environ.get("HERMES_HOME", Path.home() / ".hermes"), never via Path.home() directly.

Pricing fixture

tests/fixtures/pricing.yaml is a committed fixture used by pricing tests. This prevents test results from depending on whatever ~/.hermes/telemetry/pricing.yaml your machine happens to have. New tests that need specific pricing data should seed it in the per-test temp dir, not rely on real files.

Where do tests write?

/tmp/pytest-of-<user>/pytest-<N>/<test_name><i>/telemetry/{telemetry.db,pricing.yaml,...}

pytest’s built-in tmp_path fixture mints this per test. Override the base dir with pytest --basetemp=DIR.

`HERMES_TELEMETRY_HOME` neutralization

HERMES_TELEMETRY_HOME outranks HERMES_HOME when resolving telemetry paths. The autouse isolate_hermes_home fixture (conftest.py) therefore DELETES HERMES_TELEMETRY_HOME per test, so a developer’s ambient value cannot override the tmp redirect and leak the suite into the real ~/.hermes/telemetry. Enforced by tests/test_isolation.py::test_conftest_neutralizes_ambient_telemetry_home.

hermes-telemetry is an independent community plugin for Hermes Agent. It is not affiliated with or endorsed by Nous Research.