test(HashMapCustomTest): add driver program for custom HashMap implementation

What
- Introduced HashMapCustomTest class to demonstrate and validate functionality of HashMapCustom<K,V>.
- Operations tested:
  - put() with new keys.
  - put() with duplicate key to update value.
  - get() to retrieve values.
  - remove() to delete a key.
  - printMap() to display buckets and entries.
  - for-each iteration over entries via Iterable support.

Why
- Provide a simple, executable test harness for HashMapCustom.
- Validate that:
  - Updates overwrite existing values.
  - Removal clears entries and subsequent get() returns null.
  - Iteration traverses all stored entries.
- Serve as documentation/example usage for developers.

How
- Created HashMapCustom<Object, Integer> instance.
- Inserted sample key-value pairs (Alice, Bob, Charlie).
- Updated Alice’s value to confirm overwrite behavior.
- Removed Bob to confirm removal behavior.
- Printed contents via printMap().
- Iterated over entries with for-each loop to demonstrate Iterable support.

Logic
- Inputs: string keys, integer values inserted via put().
- Outputs: integer values retrieved via get(), null for missing keys, and formatted entries from printMap()/iteration.
- Execution flow:
  1. Insert/update → check key uniqueness and collision handling.
  2. Retrieve values by key to verify correctness.
  3. Remove entry → verify absence.
  4. Print and iterate → show map’s internal state and traversal.

Real-life applications
- Educational demonstration of custom HashMap operations.
- Quick validation of custom map implementation.
- Useful for regression testing as HashMapCustom evolves.

Notes
- Currently uses Object keys and Integer values; type parameters can be adjusted for specific use cases.
- Output order is not guaranteed (depends on hashing and bucket distribution).
- This test is not exhaustive (e.g., no explicit load factor / resize testing), but covers basic CRUD operations and iteration.

Signed-off-by: https://github.com/Someshdiwan <someshdiwan369@gmail.com>

Author: Someshdiwan

Section 25 Collections Frameworks/Map Interface/HashMap/Custom HashMap/src/CustomHashMap/HashMapCustomTest.java

@@ -0,0 +1,28 @@
+package CustomHashMap;
+
+/* Test runner for HashMapCustom. */
+
+public class HashMapCustomTest {
+    public static void main(String[] args) {
+        HashMapCustom<Object, Integer> map = new HashMapCustom<Object, Integer>();
+        map.put("Alice", 25);
+        map.put("Bob", 30);
+        map.put("Charlie", 35);
+        map.put("Alice", 28); // Update value for "Alice"
+
+        System.out.println("Value of Alice: " + map.get("Alice")); // 28
+        System.out.println("Value of Bob: " + map.get("Bob"));       // 30
+        System.out.println("Value of Charlie: " + map.get("Charlie"));// 35
+
+        map.remove("Bob");
+        System.out.println("Value of Bob after removal: " + map.get("Bob")); // null
+
+        System.out.println("\nCustom HashMap Contents:");
+        map.printMap();
+
+        System.out.println("\nIterating over CustomHashMap entries:");
+        for (HashMapCustom.Entry<Object, Integer> entry : map) {
+            System.out.println(entry.getKey() + " -> " + entry.getValue());
+        }
+    }
+}