[29/N] Add unit tests for BTree, TreeMap, SkipList, and DisjointSet algorithms

[karkir0003]

🥞 Stack

1. ⬅️ [1/N] Update CI to run frontend unit tests #91 (Add test infrastructure and Jest setup)
2. ⬅️ [2/N] Configure React Testing Library and Setup Tests #92 (Add unit tests for Footer, Header, and Blob components)
3. ⬅️ [3/N] Add unit tests for SideButton component #94 (Add unit tests for AlgorithmNotFound404 component)
4. ⬅️ [4/N] Add unit tests for SearchFilter component #95 (Add unit tests for Pseudocode component)
5. ⬅️ [5/N] Add unit tests for Header and Footer components #96 (Add unit tests for AlgoSection component)
6. ⬅️ [6/N] Add unit tests for Blob mascot component #97 (Add unit tests for ModalSidebarSectionTab component)
7. ⬅️ [7/N] Add unit tests for AboutScreen screen #98 (Add unit tests for BigOModal component)
8. ⬅️ [8/N] Add integration tests for HomeScreen screen #99 (Add unit tests for InfoModals component)
9. ⬅️ [9/N] Add unit tests for AlgorithmNotFound404 component #100 (Add unit tests for SideButton component)
10. ⬅️ [10/N] Add integration tests for AlgoScreen screen #101 (Add unit tests for SearchFilter component)
11. ⬅️ [11/N] Add unit tests for ModalSidebarSectionTab component #102 (Add unit tests for HomeScreen)
12. ⬅️ [12/N] Add unit tests for BigOModal component #103 (Add unit tests for AboutScreen)
13. ⬅️ [13/N] Add unit tests for Pseudocode component #104 (Add unit tests for AlgoScreen)
14. ⬅️ [14/N] Add unit and integration tests for AlgoSection component #105 (Add unit tests for AlgoList registry)
15. ⬅️ [15/N] Add unit and integration tests for root App component #106 (Add unit and integration tests for root App component)
16. ⬅️ [16/N] Add unit tests for animation events and undo functions #107 (Add unit tests for animation events and undo functions)
17. ⬅️ [17/N] Add unit tests for AnimatedObject, AnimatedCircle, and AnimatedHighlightCircle #108 (Add unit tests for AnimatedObject, AnimatedCircle, and AnimatedHighlightCircle)
18. ⬅️ [18/N] Add unit tests for AnimatedRectangle, AnimatedLabel, and AnimatedLine #109 (Add unit tests for AnimatedRectangle, AnimatedLabel, and AnimatedLine)
19. ⬅️ [19/N] Add unit tests for AnimatedLinkedListNode, AnimatedDoublyLinkedListNode, and AnimatedCircularlyLinkedListNode #110 (Add unit tests for AnimatedLinkedListNode, AnimatedDoublyLinkedListNode, and AnimatedCircularlyLinkedListNode)
20. ⬅️ [20/N] Add unit tests for AnimatedBTreeNode and AnimatedSkipListNode #111 (Add unit tests for AnimatedBTreeNode and AnimatedSkipListNode)
21. ⬅️ [21/N] Add unit tests for ObjectManager #112 (Add unit tests for ObjectManager)
22. ⬅️ [22/N] Add unit tests for AnimationMain #113 (Add unit tests for AnimationMain)
23. ⬅️ [23/N] Add unit tests for algo util helpers (PriorityQueue, SkipListHeads, GraphValues) #114 (Add unit tests for algo util helpers (PriorityQueue, SkipListHeads, GraphValues))
24. ⬅️ [24/N] Add unit tests for base Algorithm class and control bar helpers #115 (Add unit tests for base Algorithm class and control bar helpers)
25. ⬅️ [25/N] Add unit tests for ArrayList algorithm #116 (Add unit tests for ArrayList algorithm)
26. ⬅️ [26/N] Add unit tests for LinkedList, DoublyLinkedList, and CircularlyLinkedList algorithms #117 (Add unit tests for LinkedList, DoublyLinkedList, and CircularlyLinkedList algorithms)
27. ⬅️ [27/N] Add unit tests for Stack, Queue, and Deque algorithms (Array and LL variants) #118 (Add unit tests for Stack, Queue, and Deque algorithms (Array and LL variants))
28. ⬅️ [28/N] Add unit tests for BST, AVL, Heap, and SplayTree algorithms #119 (Add unit tests for BST, AVL, Heap, and SplayTree algorithms)
29. 👉 #CURRENT — Add unit tests for BTree, TreeMap, SkipList, and DisjointSet algorithms (this PR)
30. ➡️ [30/N] Add unit tests for Hash, OpenHash, ClosedHash, and NonLinearProbing algorithms #121 (Add unit tests for Hash, OpenHash, ClosedHash, and NonLinearProbing algorithms)

---

Addresses #93

Context

Adds comprehensive unit test coverage for the advanced search tree, skip list, and disjoint set algorithm visualizers:

• BTree.js: B-Tree multi-element search tree with node splits, promotions, searches, predecessor/successor deletions, and custom tree string builder.
• TreeMap.js: Key-value balanced map (AVL-backed) with put, get, remove, and rotation rebalancing.
• SkipList.js: Multi-level probabilistic skip list with tower additions, coin flips, forward/down pointer traversal, and deletions.
• DisjointSet.js: Disjoint set / union-find visualizer with dual array and tree representations, union-by-rank, and path compression.

Changes Made

• Introduced src/algo/__tests__/BTree.test.js:
  • Control registration (insert, delete, find, print, random, clear, split index, pred/succ, build tree).
  • Multi-element node insertions causing splits and tree growth.
  • Preemptive split on full nodes.
  • Search (find present, miss, boundary bounds).
  • Deletions: leaf keys, internal keys with predecessor / successor replacement.
  • buildTree parsing pipe-and-comma format ("2,9,13|1|5,6,7|11,12|14,16") and problem detection (treeHasProblem).
  • URL parameter deserialization (promote, predSucc, data).
• Introduced src/algo/__tests__/TreeMap.test.js:
  • Key-value pair insertion, duplicate key updates.
  • LL, RR, LR, and RL rotations maintaining AVL balance properties.
  • Key search (hits and misses across subtrees).
  • Deletions: leaf nodes, single-child nodes, two-child nodes with predecessor or successor.
  • Dynamic resizing, string vs numeric key comparisons, URL data loading.
• Introduced src/algo/__tests__/SkipList.test.js:
  • Skip list tower initialization with negative and positive infinity headers.
  • Insertion with specified heads (addWithHeads) and random coin flips (addRandomly).
  • Sorted multi-level link maintenance and duplicate key handling.
  • Column shifting on node removal.
  • Key search (get), random population, and reset.
• Introduced src/algo/__tests__/DisjointSet.test.js:
  • Array and tree dual visualizer representations for 16 elements.
  • Union operations merging disjoint sets, self-unions.
  • Union-by-rank (rank as number of nodes and rank as estimated height).
  • Find operations with path compression updating root references and links.
  • Component size computation (getSizes), reset, and clear.

Test Plan

• Ran npm test -- --watchAll=false (all 4 new test suites pass, 59 unit tests passing).
• Ran npm run lint and npm run prettier (0 errors, 0 warnings).