[ravindra-RKB]

Description

This PR introduces comprehensive unit tests for TOrdCollection in core/cont/test/TOrdCollectionTest.cxx.

TOrdCollection is an ordered sequence container backed by an array with gap-buffer semantics, actively used across ROOT subsystems. Previously, there was no dedicated Google Test coverage for it in core/cont/test.

The new test suite covers:

• Default and custom capacity construction and empty collection boundary behavior.
• Sequential and positional insertions (AddFirst, AddLast, AddAt, AddBefore, AddAfter).
• In-place element replacement (PutAt).
• Removal operations (Remove, RemoveAt) across boundaries (head, middle, tail).
• Relative element navigation (First, Last, Before, After, IndexOf).
• Sorting and binary search (Sort, BinarySearch).
• Ownership semantics, object lifetime, and cleanup (SetOwner, Clear, Delete).
• Forward and reverse iteration (TIter and TOrdCollectionIter).

Checklist

• Code follows the project's style conventions and formatting guidelines.
• New unit tests have been added and verified locally.
• Tested against MSVC with /W4 /WX with zero warnings.

[github-actions]

Test Results

    23 files      23 suites   3d 11h 26m 54s ⏱️
 3 867 tests  3 864 ✅ 0 💤  3 ❌
73 598 runs  73 552 ✅ 0 💤 46 ❌

For more details on these failures, see this check.

Results for commit 5c066eb.

[pcanal]

When testing error cases that will issue an error message, please use ROOT::TestSupport::CheckDiagsRAII.

[ravindra-RKB]

Updated! I have removed the unhandled illegal-index calls from DefaultConstructor and added a dedicated OutOfBoundsAndIllegalIndices test using ROOT::TestSupport::CheckDiagsRAII to verify error diagnostics for illegal indices (At, PutAt) as well as unsorted BinarySearch.