Add tests for recursive merge sort (#3510)

src/main/java/com/thealgorithms/sorts/MergeSortRecursive.java

@@ -12,9 +12,9 @@ public class MergeSortRecursive {
         this.arr = arr;
     }
 
-    public void mergeSort() {
+    public List<Integer> mergeSort() {
         List<Integer> arrSorted = merge(arr);
-        System.out.println(arrSorted);
+        return arrSorted;
     }
 
     private static List<Integer> merge(List<Integer> arr) {

src/test/java/com/thealgorithms/sorts/HeapSortTest.java

@@ -0,0 +1,35 @@
+package com.thealgorithms.sorts;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+
+import org.junit.jupiter.api.Test;
+
+public class HeapSortTest {
+	
+	private HeapSort heapSort = new HeapSort();
+	
+	@Test
+    void testHeapSortCase1() {
+        Integer[] array = { 49, 4, 36, 9, 144, 1 };
+        Integer[] sorted = heapSort.sort(array);
+        Integer[] expected = { 1, 4, 9, 36, 49, 144 };
+        assertArrayEquals(expected, sorted);
+    }
+	
+	@Test
+    void testHeapSortCase2() {
+        Integer[] array = { };
+        Integer[] sorted = heapSort.sort(array);
+        Integer[] expected = { };
+        assertArrayEquals(expected, sorted);
+    }
+	
+	@Test
+    void testHeapSortCase3 () {
+        Integer[] array = { -3, 5, 3, 4, 3, 7, 40, -20, 30, 0 };
+        Integer[] sorted = heapSort.sort(array);
+        Integer[] expected = { -20, -3, 0, 3, 3, 4, 5, 7, 30, 40 };
+        assertArrayEquals(expected, sorted);
+    }
+
+}

src/test/java/com/thealgorithms/sorts/MergeSortRecursiveTest.java

@@ -0,0 +1,35 @@
+package com.thealgorithms.sorts;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+import org.junit.jupiter.api.Test;
+
+public class MergeSortRecursiveTest {
+	
+//	private MergeSortRecursive mergeSortRecursive = new MergeSortRecursive();
+	
+	@Test
+	void testMergeSortRecursiveCase1 () {
+		MergeSortRecursive mergeSortRecursive = new MergeSortRecursive(Arrays.asList(5, 12, 9, 3, 15, 88));
+		
+		List<Integer> expected = Arrays.asList(3, 5, 9, 12, 15, 88);
+		List<Integer> sorted = mergeSortRecursive.mergeSort();
+		
+		assertEquals(expected, sorted);
+	}
+	
+	@Test
+	void testMergeSortRecursiveCase2 () {
+		MergeSortRecursive mergeSortRecursive = new MergeSortRecursive(Arrays.asList(-3, 5, 3, 4, 3, 7, 40, -20, 30, 0));
+		
+		List<Integer> expected = Arrays.asList(-20, -3, 0, 3, 3, 4, 5, 7, 30, 40);
+		List<Integer> sorted = mergeSortRecursive.mergeSort();
+		
+		assertEquals(expected, sorted);
+	}
+
+}