Unit tests for individual LLM providers.

Name of the test file is the name of the LLM provider - e.g. `test_openai.py` is for OpenAI.

## Redis-backed VCR cache

Every test in this directory is auto-decorated with `@pytest.mark.vcr` (via
`conftest.py`). The first time a test runs we hit the live provider and
record the HTTP exchange into Redis under
`litellm:vcr:cassette:<test_id>`. Every subsequent run within 24h replays
from Redis without touching the network. The 24h TTL means each new day's
first run records again, so upstream API drift surfaces within a day.

The persister, header scrubbing, and 2xx-only filtering are defined in
`tests/_vcr_redis_persister.py`. Files that already use `respx` (which
patches the same httpx transport vcrpy does) are excluded from the
auto-marker — see `_RESPX_CONFLICTING_FILES` in `conftest.py`.

Requests to `localhost`, `127.0.0.1`, or `0.0.0.0` are never recorded or
replayed (`ignore_localhost` in `vcr_config_dict()`): a server the test
process starts itself on an ephemeral port is not a provider, and a cassette
entry for it would replay against whichever later test lands on that port

The same VCR cache is used by other test directories that exercise live
provider APIs. The reusable conftest plumbing lives in
`tests/_vcr_conftest_common.py` and is wired into:

- `tests/llm_translation/`
- `tests/llm_responses_api_testing/`
- `tests/audio_tests/`
- `tests/batches_tests/`
- `tests/guardrails_tests/`
- `tests/image_gen_tests/`
- `tests/litellm_utils_tests/`
- `tests/local_testing/` (covers `local_testing_part1`, `local_testing_part2`,
  `litellm_router_testing`, `litellm_assistants_api_testing`,
  `langfuse_logging_unit_tests`)
- `tests/logging_callback_tests/`
- `tests/pass_through_unit_tests/`
- `tests/router_unit_tests/`
- `tests/unified_google_tests/`

Test directories that run LiteLLM proxy in Docker (e.g. `build_and_test`,
`proxy_logging_guardrails_model_info_tests`, `proxy_store_model_in_db_tests`)
are intentionally not included: VCR.py patches the in-process httpx
transport, so it cannot intercept the LLM calls that originate inside the
Docker container.

### Required environment

`CASSETTE_REDIS_URL` — separate Redis instance from the application
Redis (`REDIS_URL`/`REDIS_HOST`) so test cassettes are not flushed by
proxy tests. Provider credentials (`ANTHROPIC_API_KEY`, `OPENAI_API_KEY`,
`AWS_*`, etc.) are needed only on cache-miss (the daily re-record), not
on replay.

### Flushing the cache

When you want the next run to re-record immediately instead of waiting
for the 24h TTL:

```bash
make test-llm-translation-flush-vcr-cache
```

### Disabling VCR

Skip the cache entirely (every call goes live, no recording):

```bash
LITELLM_VCR_DISABLE=1 uv run pytest tests/llm_translation/test_<file>.py
```