else branch is unreachable dead code

_check_custom_proxy for Vertex AI always returns "{api_base}:{endpoint}" (i.e., …:cancel), so api_base will always end with :cancel and the else branch is never executed. If the :cancel suffix can genuinely appear in the middle of a custom URL, the else branch handles it correctly, but in practice this path is dead.

More importantly, if _check_custom_proxy were ever to return a URL that contains no :cancel token at all (e.g., due to a future refactor), then:

api_base.rsplit(":cancel", 1)[0]  # returns the full api_base unchanged

…causing retrieve_api_base == api_base (the cancel endpoint). The follow-up GET would then hit the :cancel endpoint instead of the retrieve endpoint, silently returning a wrong response or an error.

Consider adding an explicit guard or an assertion to make this invariant clear:

if api_base.endswith(":cancel"):
    retrieve_api_base = api_base.removesuffix(":cancel")
elif ":cancel" in api_base:
    retrieve_api_base = api_base.rsplit(":cancel", 1)[0].rstrip("/")
else:
    # _check_custom_proxy always appends ":cancel"; reaching here is a bug
    raise ValueError(
        f"cancel_batch: expected api_base to contain ':cancel', got: {api_base!r}"
    )

cast(Any, ...) silences a type error rather than fixing it

Using cast(Any, managed_files_obj) removes all type-checking on the subsequent method call. If managed_files_obj gains a new return type or if list_user_batches is renamed, this cast will silently hide the discrepancy at type-check time.

A better approach would be to use a proper Protocol or TypeVar for managed_files_obj, or at minimum cast it to the specific type that exposes list_user_batches, rather than casting to Any.

Custom proxy retrieve URL is missing the batch_id

When a caller supplies a custom api_base (e.g. "https://my-proxy.example.com"), _check_custom_proxy constructs:

api_base → "https://my-proxy.example.com:cancel"

Stripping :cancel then yields:

retrieve_api_base → "https://my-proxy.example.com"   # ← batch_id not included

In contrast, when api_base=None the default URL already has the batch_id baked in (…/batchPredictionJobs/{batch_id}:cancel), so the strip works correctly.

The follow-up GET to retrieve_api_base will therefore hit the proxy root — not the specific batch resource — causing the retrieve step to return an unexpected response or 404.

The custom-proxy path should include the batch_id before the :cancel suffix is added, for example by constructing the base path first:

if api_base is not None:
    # Build the per-batch base URL from the custom proxy, then append :cancel
    per_batch_api_base = f"{api_base.rstrip('/')}/{batch_id}"
    cancel_url = f"{per_batch_api_base}:cancel"
else:
    per_batch_api_base = retrieve_api_base_default
    cancel_url = cancel_api_base_default

_, api_base = self._check_custom_proxy(
    api_base=None,   # already handled above
    ...
    url=cancel_url,
    ...
)
retrieve_api_base = per_batch_api_base

The existing test test_vertex_ai_cancel_batch_custom_proxy_retrieve_url does not assert that the batch_id (123456) is present in the get_url, so this bug is not caught today.

max_retries parameter is accepted but silently ignored

max_retries is declared as a parameter of cancel_batch (and propagated from litellm/batches/main.py) but is never passed to _get_httpx_client(), get_async_httpx_client(), or used anywhere else in the method body. This is inconsistent with the caller's intent and means retry logic is never applied.

If retry support is intentionally deferred, consider removing the parameter from the signature to avoid a misleading contract, or add a # TODO: comment so it is not forgotten.

Empty test body — always passes trivially

test_vertex_ai_cancel_batch_forwards_timeout contains only a docstring with no assertions or test logic. The function body is empty (implicit return None), so it will always pass regardless of actual behaviour, providing zero regression protection.

The test should verify that the timeout argument is forwarded to sync_handler.post(...). The implementation should follow the same pattern used in test_vertex_ai_cancel_batch — mock _get_httpx_client and _ensure_access_token, call handler.cancel_batch(...) with a specific timeout value (e.g. 42.0), then assert:

post_call_kwargs = mock_client.return_value.post.call_args.kwargs
assert post_call_kwargs["timeout"] == 42.0

Without this assertion the test provides no guarantee that callers' timeout settings are honoured.

Rule Used: # Code Review Rule: Mock Test Integrity

What:... (source)