Add tests, remove main in UnionFind (#5678)

src/test/java/com/thealgorithms/searches/UnionFindTest.java

@@ -0,0 +1,81 @@
+package com.thealgorithms.searches;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+class UnionFindTest {
+    private UnionFind uf;
+
+    @BeforeEach
+    void setUp() {
+        uf = new UnionFind(10); // Initialize with 10 elements
+    }
+
+    @Test
+    void testInitialState() {
+        // Verify that each element is its own parent and rank is 0
+        assertEquals("p [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] r [0, 0, 0, 0, 0, 0, 0, 0, 0, 0]\n", uf.toString());
+        assertEquals(10, uf.count(), "Initial count of disjoint sets should be 10.");
+    }
+
+    @Test
+    void testUnionOperation() {
+        uf.union(0, 1);
+        uf.union(1, 2);
+        assertEquals(8, uf.count(), "Count should decrease after unions.");
+        assertEquals(0, uf.find(2), "Element 2 should point to root 0 after unions.");
+    }
+
+    @Test
+    void testUnionWithRank() {
+        uf.union(0, 1);
+        uf.union(1, 2); // Make 0 the root of 2
+        uf.union(3, 4);
+        uf.union(4, 5); // Make 3 the root of 5
+        uf.union(0, 3); // Union two trees
+
+        assertEquals(5, uf.count(), "Count should decrease after unions.");
+        assertEquals(0, uf.find(5), "Element 5 should point to root 0 after unions.");
+    }
+
+    @Test
+    void testFindOperation() {
+        uf.union(2, 3);
+        uf.union(4, 5);
+        uf.union(3, 5); // Connect 2-3 and 4-5
+
+        assertEquals(2, uf.find(3), "Find operation should return the root of the set.");
+        assertEquals(2, uf.find(5), "Find operation should return the root of the set.");
+    }
+
+    @Test
+    void testCountAfterMultipleUnions() {
+        uf.union(0, 1);
+        uf.union(2, 3);
+        uf.union(4, 5);
+        uf.union(1, 3); // Connect 0-1-2-3
+        uf.union(5, 6);
+
+        assertEquals(5, uf.count(), "Count should reflect the number of disjoint sets after multiple unions.");
+    }
+
+    @Test
+    void testNoUnion() {
+        assertEquals(10, uf.count(), "Count should remain 10 if no unions are made.");
+    }
+
+    @Test
+    void testUnionSameSet() {
+        uf.union(1, 2);
+        uf.union(1, 2); // Union same elements again
+
+        assertEquals(9, uf.count(), "Count should not decrease if union is called on the same set.");
+    }
+
+    @Test
+    void testFindOnSingleElement() {
+        assertEquals(7, uf.find(7), "Find on a single element should return itself.");
+    }
+}