Enhancing DisjointSetUnion data structure (#4366)

* Enhancing DisjointSetUnion data structure

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Co-authored-by: Bama Charan Chhandogi <b.c.chhandogi@gmail.com>

src/test/java/com/thealgorithms/datastructures/disjointsetunion/DisjointSetUnionTest.java

@@ -0,0 +1,51 @@
+package com.thealgorithms.datastructures.disjointsetunion;
+
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+public class DisjointSetUnionTest {
+
+    @Test
+    public void testMakeSet() {
+        DisjointSetUnion<Integer> dsu = new DisjointSetUnion<>();
+        Node<Integer> node = dsu.makeSet(1);
+        assertNotNull(node);
+        Assertions.assertEquals(node, node.parent);
+    }
+
+    @Test
+    public void testUnionFindSet() {
+        DisjointSetUnion<Integer> dsu = new DisjointSetUnion<>();
+        Node<Integer> node1 = dsu.makeSet(1);
+        Node<Integer> node2 = dsu.makeSet(2);
+        Node<Integer> node3 = dsu.makeSet(3);
+        Node<Integer> node4 = dsu.makeSet(4);
+
+        dsu.unionSets(node1, node2);
+        dsu.unionSets(node3, node2);
+        dsu.unionSets(node3, node4);
+        dsu.unionSets(node1, node3);
+
+        Node<Integer> root1 = dsu.findSet(node1);
+        Node<Integer> root2 = dsu.findSet(node2);
+        Node<Integer> root3 = dsu.findSet(node3);
+        Node<Integer> root4 = dsu.findSet(node4);
+
+        Assertions.assertEquals(node1, node1.parent);
+        Assertions.assertEquals(node1, node2.parent);
+        Assertions.assertEquals(node1, node3.parent);
+        Assertions.assertEquals(node1, node4.parent);
+
+        Assertions.assertEquals(node1, root1);
+        Assertions.assertEquals(node1, root2);
+        Assertions.assertEquals(node1, root3);
+        Assertions.assertEquals(node1, root4);
+
+        Assertions.assertEquals(1, node1.rank);
+        Assertions.assertEquals(0, node2.rank);
+        Assertions.assertEquals(0, node3.rank);
+        Assertions.assertEquals(0, node4.rank);
+    }
+}