test: add unit test for null array handling in TournamentSort

Author: GziXnine

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

@@ -1,7 +1,17 @@
 package com.thealgorithms.sorts;
 
+import static org.junit.jupiter.api.Assertions.assertNull;
+
+import org.junit.jupiter.api.Test;
+
 public class TournamentSortTest extends SortingAlgorithmTest {
 
+    @Test
+    void shouldAcceptWhenNullArrayIsPassed() {
+        Integer[] array = null;
+        assertNull(getSortAlgorithm().sort(array));
+    }
+
     @Override
     SortAlgorithm getSortAlgorithm() {
         return new TournamentSort();