[core] Add essential unit tests for TMap

[ravindra-RKB]

This Pull request:

Introduces essential unit tests for the TMap associative container in core/cont.

Changes or fixes:

• Adds unit tests in core/cont/test/TMapTest.cxx covering:
  • Default initialization, capacity, and empty state checks
  • Key-value insertion and lookup by string key and object pointer (GetValue, operator(), FindObject)
  • Deliberate hash collision handling and bucket collision tracking
  • Entry removal via Remove (returning key) and RemoveEntry (returning TPair*)
  • Independent ownership semantics (SetOwner vs SetOwnerValue), removal cleanup, and DeleteEntry
  • Dynamic capacity expansion via Rehash
  • Lifecycle memory management across non-owner Clear(), DeleteKeys(), DeleteValues(), DeleteAll(), and owner Clear()
  • Forward traversal using TIter
• Registers TMapTest in core/cont/test/CMakeLists.txt

Checklist:

• tested changes locally
• updated the docs (if necessary)

[pcanal]

Adds comprehensive test coverage in core/cont/test/TMapTest.cxx covering:

Is this PR meant to be comprehensive?

[pcanal]

Dynamic capacity expansion and collision behavior via Rehash

The “collision behavior” test could be enhanced to deliberately create a collision; it currently only checks Collisions() for ordinary keys.

Also the ownership tests could cover both SetOwner() and SetOwnerValue() independently, or removal behavior when ownership is enabled.

[ravindra-RKB]

Thanks for the feedback @pcanal!

• Updated the PR description: these tests are focused on covering the essential and primary usage patterns of TMap.
• Added a dedicated HashCollision test with a custom key class that forces identical hash values to explicitly verify bucket collision counts, lookup resolution under collision, and post-removal bucket counts.
• Added an OwnershipIndependent test covering SetOwner() and SetOwnerValue() independently, verifying that value ownership triggers value cleanup on Remove(), and checking selective key/value deletion on Clear() and DeleteEntry().

[github-actions]

Test Results

0 tests   0 ✅  0s ⏱️
0 suites  0 💤
0 files    0 ❌

Results for commit 564e1bb.

♻️ This comment has been updated with latest results.

[pcanal]

Side note (if you did not already read it), check https://github.com/root-project/root/blob/master/CONTRIBUTING.md

[ravindra-RKB]

Thanks for pointing that out @pcanal. I've re-read CONTRIBUTING.md, particularly the guidelines on AI disclosure and testing standards.

Regarding the previous test failure, my previous attempt tried forcing a small capacity (TMap(3, 0)) without realizing that THashTable enforces a minimum capacity of 17 (prime 19 via kInitHashTableCapacity), so the keys ended up in separate buckets.

I have updated the test with a helper class that returns a fixed hash value and overrides IsEqual(). This guarantees a bucket collision regardless of table size, and verifies that Collisions(), key lookup, and removal behave as expected under collision. All tests compile cleanly with /W4 and adhere to clang-format.