test: add JUnit tests for StringRotation

Author: konduri-lakshmi-prasanna

src/main/java/com/thealgorithms/strings/StringRotationTest.java

@@ -0,0 +1,28 @@
+package com.thealgorithms.strings;
+
+import static org.junit.jupiter.api.Assertions.*;
+import org.junit.jupiter.api.Test;
+
+public class StringRotationTest {
+
+    @Test
+    void testValidRotation() {
+        assertTrue(StringRotation.isRotation("waterbottle", "erbottlewat"));
+    }
+
+    @Test
+    void testInvalidRotation() {
+        assertFalse(StringRotation.isRotation("hello", "world"));
+    }
+
+    @Test
+    void testDifferentLengths() {
+        assertFalse(StringRotation.isRotation("abc", "abcd"));
+    }
+
+    @Test
+    void testNullInput() {
+        assertFalse(StringRotation.isRotation(null, "abc"));
+        assertFalse(StringRotation.isRotation("abc", null));
+    }
+}