Add DarkSort Algorithm (#6141)

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

@@ -0,0 +1,74 @@
+package com.thealgorithms.sorts;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+
+import org.junit.jupiter.api.Test;
+
+class DarkSortTest {
+
+    @Test
+    void testSortWithIntegers() {
+        Integer[] unsorted = {5, 3, 8, 6, 2, 7, 4, 1};
+        Integer[] expected = {1, 2, 3, 4, 5, 6, 7, 8};
+
+        DarkSort darkSort = new DarkSort();
+        Integer[] sorted = darkSort.sort(unsorted);
+
+        assertArrayEquals(expected, sorted);
+    }
+
+    @Test
+    void testEmptyArray() {
+        Integer[] unsorted = {};
+        Integer[] expected = {};
+
+        DarkSort darkSort = new DarkSort();
+        Integer[] sorted = darkSort.sort(unsorted);
+
+        assertArrayEquals(expected, sorted);
+    }
+
+    @Test
+    void testSingleElementArray() {
+        Integer[] unsorted = {42};
+        Integer[] expected = {42};
+
+        DarkSort darkSort = new DarkSort();
+        Integer[] sorted = darkSort.sort(unsorted);
+
+        assertArrayEquals(expected, sorted);
+    }
+
+    @Test
+    void testAlreadySortedArray() {
+        Integer[] unsorted = {1, 2, 3, 4, 5};
+        Integer[] expected = {1, 2, 3, 4, 5};
+
+        DarkSort darkSort = new DarkSort();
+        Integer[] sorted = darkSort.sort(unsorted);
+
+        assertArrayEquals(expected, sorted);
+    }
+
+    @Test
+    void testDuplicateElementsArray() {
+        Integer[] unsorted = {4, 2, 7, 2, 1, 4};
+        Integer[] expected = {1, 2, 2, 4, 4, 7};
+
+        DarkSort darkSort = new DarkSort();
+        Integer[] sorted = darkSort.sort(unsorted);
+
+        assertArrayEquals(expected, sorted);
+    }
+
+    @Test
+    void testNullArray() {
+        Integer[] unsorted = null;
+
+        DarkSort darkSort = new DarkSort();
+        Integer[] sorted = darkSort.sort(unsorted);
+
+        assertNull(sorted, "Sorting a null array should return null");
+    }
+}