CodeQL 11: chore(tests): replace Returns((T?)null) casts with ReturnsNull()

[rlorenzo]

Summary

Closes ~19 cs/useless-upcast alerts in test/** by replacing the NSubstitute pattern .Returns((SomeType?)null) with the dedicated .ReturnsNull() extension from NSubstitute.ReturnsExtensions.

Why

The explicit (T?)null cast existed because the bare .Returns(null) call is ambiguous between NSubstitute's Returns<T>(T) and Returns<T>(Func<CallInfo, T>) overloads, but the cast itself trips the cs/useless-upcast rule (CodeQL sees the receiver's return type, so the cast is "redundant from the type system's POV"). .ReturnsNull() is the canonical NSubstitute idiom for this case - it disambiguates without a cast and makes the test intent clearer.

Files (18)

• ClinicalSchedulerTestBase, IntegrationTestBase
• CourseRelationshipsControllerTests, CoursesControllerTests, EffortIntegrationTestBase, EffortRecordsControllerTests, EffortTypesControllerTests, InstructorsControllerTests, PercentagesControllerTests, PercentAssignTypesControllerTests, ReportsControllerTests, UnitsControllerTests, VerificationControllerTests, VerificationServiceTests
• RolesTests
• EmailServiceTests
• EmergencyContactControllerTests, PhotoGalleryControllerTest

Each file got a using NSubstitute.ReturnsExtensions; added.

Context

Eleventh in the CodeQL N: cleanup series. Earlier task #9 had marked these as wontfix-by-design - that was wrong. ReturnsNull() is the correct fix.

Test plan

• npm run test:backend - 1946 tests passing
• Pre-commit lint+test+verify all passed
• CodeQL workflow on this PR shows the test/Effort/cs/useless-upcast alerts closed

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[codecov-commenter]

Bundle Report

Bundle size has no change ✅

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 42.96%. Comparing base (38de1ad) to head (183283a).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #197   +/-   ##
=======================================
  Coverage   42.96%   42.96%           
=======================================
  Files         877      877           
  Lines       51468    51468           
  Branches     4802     4802           
=======================================
  Hits        22113    22113           
  Misses      28831    28831           
  Partials      524      524           

Flag	Coverage Δ
backend	43.04% <ø> (ø)
frontend	41.34% <ø> (ø)

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