test(router): assert the auto-router max_input_chars kwarg

[yuneng-berri]

TLDR

Problem this solves:

• A test on litellm_internal_staging has been failing since fix(auto-router): stop the embedding model's context window from failing long requests #35956
• The AutoRouter mock assertion never learned about max_input_chars

How it solves it:

• Add the missing kwarg to the expected constructor call
• Assert the shared constant, not the literal 2000

Relevant issues

Linear ticket

Pre-Submission checklist

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• I have added meaningful tests
• My PR passes all CI/CD checks (e.g., lint, format, unit tests)
• My PR's scope is as isolated as possible; it only solves 1 specific problem
• I have received a Greptile Confidence Score of at least 4/5 before requesting a maintainer review (Greptile reviews automatically once the PR is opened; only comment @greptileai to re-request a review after pushing changes)

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Screenshots / Proof of Fix

This PR is test-only. git diff --stat c1fa15132b..HEAD touches exactly one file under tests/, no runtime code, so there is no proxy behavior to curl before and after: the routing behavior the assertion guards is identical on both commits

Before, on litellm_internal_staging at c1fa15132b with no local changes:

$ PYTHONPATH=$PWD python -m pytest tests/router_unit_tests/test_router_helper_utils.py -q
FAILED tests/router_unit_tests/test_router_helper_utils.py::test_init_auto_router_deployment_success
1 failed, 141 passed, 8 warnings in 114.13s (0:01:54)

with

E  Expected: AutoRouter(..., litellm_router_instance=<litellm.router.Router object at 0x11dd68c20>)
E    Actual: AutoRouter(..., litellm_router_instance=<litellm.router.Router object at 0x11dd68c20>, max_input_chars=2000)

After, at 495eb7e7f4:

$ PYTHONPATH=$PWD python -m pytest tests/router_unit_tests/test_router_helper_utils.py -q
142 passed, 8 warnings in 93.58s (0:01:33)

To confirm the updated assertion still has teeth rather than just matching whatever the code does, I dropped max_input_chars= from the AutoRouter(...) call in litellm/router.py at 495eb7e7f4 and reran, and the test went red again:

FAILED tests/router_unit_tests/test_router_helper_utils.py::test_init_auto_router_deployment_success
1 failed in 0.13s

Type

✅ Test

Changes

#35956 gave AutoRouter.__init__ a max_input_chars parameter and started passing it from Router.init_auto_router_deployment, which caps how much of a prompt reaches the embedding model. That change was intentional and stays as is. What it missed was tests/router_unit_tests/test_router_helper_utils.py, whose assert_called_once_with on the constructor still spelled out the old kwarg set, so the test has been red on staging ever since and is unrelated to whatever branch a contributor happens to be on

The passthrough is already covered behaviorally by TestAutoRouterMaxInputCharsWiring in tests/test_litellm/test_router.py, which asserts both that a deployment's auto_router_max_input_chars reaches the registered AutoRouter and that omitting it falls back to the shared default. Duplicating that here would add no signal, so this PR only brings the stale expectation back in line. It asserts DEFAULT_AUTO_ROUTER_MAX_INPUT_CHARS instead of hardcoding 2000 so that tuning the default does not break this test a second time

Final Attestation

• The tests check the right things, including the edge cases, and regressions in the respective real-world customer use-cases are not possible after this PR

[greptile-apps]

Greptile Summary

This test-only PR updates the AutoRouter constructor assertion to include the shared default input-character limit.

• Imports DEFAULT_AUTO_ROUTER_MAX_INPUT_CHARS.
• Verifies that Router.init_auto_router_deployment passes the shared default to AutoRouter.

Confidence Score: 5/5

The PR appears safe to merge, with no actionable defects identified.

The changed assertion now matches the intentional AutoRouter default passthrough, while separate tests continue to cover both configured and fallback values.

Important Files Changed

Filename	Overview
tests/router_unit_tests/test_router_helper_utils.py	Correctly updates the stale mock assertion using the shared constant without weakening coverage or changing runtime behavior.

_{Reviews (1): Last reviewed commit: "test(router): assert the auto-router max..." | Re-trigger Greptile}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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