testing: improve test coverage CursorLinkedListTest (#6428)

* testing: improve test coverage CursorLinkedListTest

* style: fix checkstyle formatting

Author: alxkm

src/test/java/com/thealgorithms/datastructures/lists/CursorLinkedListTest.java

@@ -109,4 +109,189 @@ void testMemoryLimitExceeded() {
             }
         });
     }
+
+    @Test
+    void testSingleElementOperations() {
+        // Test operations with just one element
+        list.append("Only");
+        assertEquals("Only", list.get(0));
+        assertEquals(0, list.indexOf("Only"));
+
+        list.remove("Only");
+        assertNull(list.get(0));
+        assertEquals(-1, list.indexOf("Only"));
+    }
+
+    @Test
+    void testDuplicateElements() {
+        // Test handling of duplicate elements
+        list.append("Duplicate");
+        list.append("Other");
+        list.append("Duplicate");
+
+        assertEquals(0, list.indexOf("Duplicate")); // Should return first occurrence
+        assertEquals("Duplicate", list.get(0));
+        assertEquals("Duplicate", list.get(2));
+
+        list.remove("Duplicate"); // Should remove first occurrence
+        assertEquals("Other", list.get(0));
+        assertEquals("Duplicate", list.get(1));
+    }
+
+    @Test
+    void testRemoveByIndexEdgeCases() {
+        list.append("First");
+        list.append("Second");
+        list.append("Third");
+
+        // Test removing invalid indices
+        list.removeByIndex(-1); // Should not crash
+        list.removeByIndex(10); // Should not crash
+
+        // Verify list unchanged
+        assertEquals("First", list.get(0));
+        assertEquals("Second", list.get(1));
+        assertEquals("Third", list.get(2));
+
+        // Test removing first element by index
+        list.removeByIndex(0);
+        assertEquals("Second", list.get(0));
+        assertEquals("Third", list.get(1));
+    }
+
+    @Test
+    void testRemoveByIndexLastElement() {
+        list.append("First");
+        list.append("Second");
+        list.append("Third");
+
+        // Remove last element by index
+        list.removeByIndex(2);
+        assertEquals("First", list.get(0));
+        assertEquals("Second", list.get(1));
+        assertNull(list.get(2));
+    }
+
+    @Test
+    void testConsecutiveOperations() {
+        // Test multiple consecutive operations
+        list.append("A");
+        list.append("B");
+        list.append("C");
+        list.append("D");
+
+        list.remove("B");
+        list.remove("D");
+
+        assertEquals("A", list.get(0));
+        assertEquals("C", list.get(1));
+        assertNull(list.get(2));
+
+        list.append("E");
+        assertEquals("E", list.get(2));
+    }
+
+    @Test
+    void testMemoryReclamation() {
+        // Test that removed elements free up memory space
+        for (int i = 0; i < 50; i++) {
+            list.append("Element" + i);
+        }
+
+        // Remove some elements
+        for (int i = 0; i < 25; i++) {
+            list.remove("Element" + i);
+        }
+
+        // Should be able to add more elements (testing memory reclamation)
+        for (int i = 100; i < 150; i++) {
+            list.append("New" + i);
+        }
+
+        // Verify some elements exist
+        assertEquals("Element25", list.get(0));
+        assertEquals("New100", list.get(25));
+    }
+
+    @Test
+    void testSpecialCharacters() {
+        // Test with strings containing special characters
+        list.append("Hello World!");
+        list.append("Test@123");
+        list.append("Special#$%");
+        list.append(""); // Empty string
+
+        assertEquals("Hello World!", list.get(0));
+        assertEquals("Test@123", list.get(1));
+        assertEquals("Special#$%", list.get(2));
+        assertEquals("", list.get(3));
+
+        assertEquals(3, list.indexOf(""));
+    }
+
+    @Test
+    void testLargeIndices() {
+        list.append("Test");
+
+        // Test very large indices
+        assertNull(list.get(Integer.MAX_VALUE));
+        assertNull(list.get(1000));
+    }
+
+    @Test
+    void testSequentialRemovalByIndex() {
+        list.append("A");
+        list.append("B");
+        list.append("C");
+        list.append("D");
+
+        // Remove elements sequentially by index
+        list.removeByIndex(1); // Remove "B"
+        assertEquals("A", list.get(0));
+        assertEquals("C", list.get(1));
+        assertEquals("D", list.get(2));
+
+        list.removeByIndex(1); // Remove "C"
+        assertEquals("A", list.get(0));
+        assertEquals("D", list.get(1));
+        assertNull(list.get(2));
+    }
+
+    @Test
+    void testAppendAfterRemoval() {
+        list.append("First");
+        list.append("Second");
+
+        list.remove("First");
+        list.append("Third");
+
+        assertEquals("Second", list.get(0));
+        assertEquals("Third", list.get(1));
+        assertEquals(1, list.indexOf("Third"));
+    }
+
+    @Test
+    void testPerformanceWithManyOperations() {
+        // Test with many mixed operations
+        for (int i = 0; i < 50; i++) {
+            list.append("Item" + i);
+        }
+
+        // Remove every other element
+        for (int i = 0; i < 50; i += 2) {
+            list.remove("Item" + i);
+        }
+
+        // Verify remaining elements
+        assertEquals("Item1", list.get(0));
+        assertEquals("Item3", list.get(1));
+        assertEquals("Item5", list.get(2));
+
+        // Add more elements
+        for (int i = 100; i < 110; i++) {
+            list.append("New" + i);
+        }
+
+        assertEquals("New100", list.get(25));
+    }
 }