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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📥 Commits

Reviewing files that changed from the base of the PR and between caa7835 and 1d66a5f.

📒 Files selected for processing (2)

• python/cuopt/cuopt/tests/linear_programming/test_incumbent_callbacks.py
• python/cuopt/cuopt/tests/socp/test_socp.py

💤 Files with no reviewable changes (2)

• python/cuopt/cuopt/tests/linear_programming/test_incumbent_callbacks.py
• python/cuopt/cuopt/tests/socp/test_socp.py

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📝 Walkthrough

Walkthrough

The PR removes one quadratic-programming test module and prunes several routing, callback, and SOCP test cases. It also simplifies imports in the affected routing test files.

Changes

Routing test pruning

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.

Incumbent callback inputs

Layer / File(s)	Summary
Callback parameter lists python/cuopt/cuopt/tests/linear_programming/test_incumbent_callbacks.py	Both incumbent-callback tests remove /mip/swath1.mps from their parametrized input lists.

SOCP regression pruning

Layer / File(s)	Summary
SOCP 1 barrier test python/cuopt/cuopt/tests/socp/test_socp.py	The module deletes the socp_1 expected constants, the build_socp_1() helper, and test_socp_1_barrier_solution().
Unsymmetric quadratic test python/cuopt/cuopt/tests/socp/test_socp.py	The module removes test_general_quadratic_unsymmetric().

Estimated code review effort: 2 (Simple) | ~10 minutes

Suggested reviewers: mlubin, Iroy30

🚥 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: removing Python regression tests in favor of C++ gtest coverage.
Description check	✅ Passed	The description matches the changeset by describing removal of Python tests and their replacement coverage in C++ gtests.
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 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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