tests: retire correctness/regression tests covered by C++ gtests

[ramakrishnap-nv]

Remove 5 Python tests that assert specific solver output values. The Python test suite should cover API behavior; correctness and regression coverage for these cases already exists in the C++ gtest suite.

Removed tests:

• test_qp.py::test_solver — asserted QP objective −32 and variable values x1=4, x2=2. QP correctness covered by cpp/tests/linear_programming/qp_test.cu; QP API covered by test_python_API.py::test_quadratic_objective_* tests.
• test_solver.py::test_solomon — asserted VRPTW objective ~1087.15 and vehicle count ≤12. Routing API covered by test_vehicle_properties.py.
• test_solver.py::test_pdptw — asserted PDP objective 13.0. Pickup-delivery pairs API covered by test_vehicle_properties.py::test_heterogenous_breaks.
• test_distance_engine.py::test_compute_cost_matrix — numerical matrix match against reference CSVs. compute_cost_matrix API covered by the kept test_compute_waypoint_sequence_* tests.
• test_distance_engine.py::test_compute_shortest_path_costs — exact matrix match against hardcoded expected values. Error-path coverage for compute_shortest_path_costs retained in test_target_locations_validity.

Also removes helper functions and imports that were only used by the deleted tests.

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ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 789b822 and caa7835.

📒 Files selected for processing (1)

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

🚧 Files skipped from review as they are similar to previous changes (1)

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

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📝 Walkthrough

Walkthrough

The quadratic-programming test module was removed, and two routing test modules were pruned. The routing files also drop unused imports and delete the shortest-path, Solomon, and PDPTW test cases.

Changes

CuOpt test module removals

Layer / File(s)	Summary
Distance-engine shortest-path tests python/cuopt/cuopt/tests/routing/test_distance_engine.py	The import block drops pandas and cuopt.routing.utils, and the shortest-path helper plus test_compute_shortest_path_costs() are removed.
Routing solver cases python/cuopt/cuopt/tests/routing/test_solver.py	The import block drops os, math, and cuopt.routing.utils, and test_solomon plus test_pdptw are removed before test_prize_collection.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main change: retiring Python tests already covered by C++ gtests.
Description check	✅ Passed	The description is directly related and accurately explains the removed tests and rationale.
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.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch ci/retire-correctness-regression-tests

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