Enhance docs, remove main, add tests in `MergeSortedArray… (#5996)

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

@@ -0,0 +1,99 @@
+package com.thealgorithms.datastructures.lists;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import org.junit.jupiter.api.Test;
+
+class MergeSortedArrayListTest {
+
+    @Test
+    void testMergeTwoSortedLists() {
+        List<Integer> listA = Arrays.asList(1, 3, 5, 7, 9);
+        List<Integer> listB = Arrays.asList(2, 4, 6, 8, 10);
+        List<Integer> result = new ArrayList<>();
+
+        MergeSortedArrayList.merge(listA, listB, result);
+
+        List<Integer> expected = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
+        assertEquals(expected, result, "Merged list should be sorted and contain all elements from both input lists.");
+    }
+
+    @Test
+    void testMergeWithEmptyList() {
+        List<Integer> listA = Arrays.asList(1, 2, 3);
+        List<Integer> listB = new ArrayList<>(); // Empty list
+        List<Integer> result = new ArrayList<>();
+
+        MergeSortedArrayList.merge(listA, listB, result);
+
+        List<Integer> expected = Arrays.asList(1, 2, 3);
+        assertEquals(expected, result, "Merged list should match listA when listB is empty.");
+    }
+
+    @Test
+    void testMergeWithBothEmptyLists() {
+        List<Integer> listA = new ArrayList<>(); // Empty list
+        List<Integer> listB = new ArrayList<>(); // Empty list
+        List<Integer> result = new ArrayList<>();
+
+        MergeSortedArrayList.merge(listA, listB, result);
+
+        assertTrue(result.isEmpty(), "Merged list should be empty when both input lists are empty.");
+    }
+
+    @Test
+    void testMergeWithDuplicateElements() {
+        List<Integer> listA = Arrays.asList(1, 2, 2, 3);
+        List<Integer> listB = Arrays.asList(2, 3, 4);
+        List<Integer> result = new ArrayList<>();
+
+        MergeSortedArrayList.merge(listA, listB, result);
+
+        List<Integer> expected = Arrays.asList(1, 2, 2, 2, 3, 3, 4);
+        assertEquals(expected, result, "Merged list should correctly handle and include duplicate elements.");
+    }
+
+    @Test
+    void testMergeWithNegativeAndPositiveNumbers() {
+        List<Integer> listA = Arrays.asList(-3, -1, 2);
+        List<Integer> listB = Arrays.asList(-2, 0, 3);
+        List<Integer> result = new ArrayList<>();
+
+        MergeSortedArrayList.merge(listA, listB, result);
+
+        List<Integer> expected = Arrays.asList(-3, -2, -1, 0, 2, 3);
+        assertEquals(expected, result, "Merged list should correctly handle negative and positive numbers.");
+    }
+
+    @Test
+    void testMergeThrowsExceptionOnNullInput() {
+        List<Integer> listA = null;
+        List<Integer> listB = Arrays.asList(1, 2, 3);
+        List<Integer> result = new ArrayList<>();
+
+        List<Integer> finalListB = listB;
+        List<Integer> finalListA = listA;
+        List<Integer> finalResult = result;
+        assertThrows(NullPointerException.class, () -> MergeSortedArrayList.merge(finalListA, finalListB, finalResult), "Should throw NullPointerException if any input list is null.");
+
+        listA = Arrays.asList(1, 2, 3);
+        listB = null;
+        List<Integer> finalListA1 = listA;
+        List<Integer> finalListB1 = listB;
+        List<Integer> finalResult1 = result;
+        assertThrows(NullPointerException.class, () -> MergeSortedArrayList.merge(finalListA1, finalListB1, finalResult1), "Should throw NullPointerException if any input list is null.");
+
+        listA = Arrays.asList(1, 2, 3);
+        listB = Arrays.asList(4, 5, 6);
+        result = null;
+        List<Integer> finalListA2 = listA;
+        List<Integer> finalListB2 = listB;
+        List<Integer> finalResult2 = result;
+        assertThrows(NullPointerException.class, () -> MergeSortedArrayList.merge(finalListA2, finalListB2, finalResult2), "Should throw NullPointerException if the result collection is null.");
+    }
+}