test routing null matrix validation

[aycsi]

Description

DataModel.add_cost_matrix routes through validate_matrix, which is expected to reject matrices containing NULL values before solve-time logic. This change adds a focused negative test to lock down that contract and prevent silent regressions during future validation.

Summary

• Add test_dist_mat_null to routing validation coverage.
• Cover the NULL input path for cost matrices in DataModel.add_cost_matrix.

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[github-actions]

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[ramakrishnap-nv]

/ok to test 6d5b75a

[ramakrishnap-nv]

/ok to test 575b1cc

[github-actions]

CI Test Summary

✅ All 22 test job(s) passed. (1 skipped)

[tmckayus]

/okay to test 89f131a

[coderabbitai]

📝 Walkthrough

Walkthrough

Changes

Routing input validation

Layer / File(s)	Summary
NULL cost matrix exception test python/cuopt/cuopt/tests/routing/test_warnings_exceptions.py	Adds coverage confirming that a cost matrix containing NULL raises the expected exception message from add_cost_matrix.

Estimated code review effort: 1 (Trivial) | ~3 minutes

Suggested reviewers: tmckayus

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately reflects the main change: adding routing validation for NULL cost matrices.
Description check	✅ Passed	The description matches the change by describing the new negative test for NULL cost matrix validation.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@python/cuopt/cuopt/tests/routing/test_warnings_exceptions.py`:
- Around line 87-90: Update the test to instantiate DataModel before the
pytest.raises block, then wrap only dm.add_cost_matrix(cost_matrix) and assert
pytest.raises(ValueError, match="^cost matrix cannot have NULL values$"). Remove
the broad Exception capture and redundant string assertion while preserving the
existing validation scenario.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Enterprise

Run ID: 43a07905-24a7-41d6-a3e3-73bc757f306b

📥 Commits

Reviewing files that changed from the base of the PR and between 91134a2 and 89f131a.

📒 Files selected for processing (1)

• python/cuopt/cuopt/tests/routing/test_warnings_exceptions.py

[tmckayus]

lgtm assuming tests pass

[ramakrishnap-nv]

/merge