test: refactor MiddleOfLinkedListTest for improved null safety and readability

Author: GziXnine

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

@@ -1,22 +1,19 @@
 package com.thealgorithms.datastructures.lists;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
-import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertNull;
 
+import java.util.Objects;
 import org.junit.jupiter.api.Test;
 
 public class MiddleOfLinkedListTest {
 
-    private static SinglyLinkedListNode listOf(int... values) {
-        if (values == null || values.length == 0) {
-            return null;
-        }
-
-        SinglyLinkedListNode head = new SinglyLinkedListNode(values[0]);
+    private static SinglyLinkedListNode listOf(int firstValue, int... remainingValues) {
+        SinglyLinkedListNode head = new SinglyLinkedListNode(firstValue);
         SinglyLinkedListNode current = head;
-        for (int i = 1; i < values.length; i++) {
-            current.next = new SinglyLinkedListNode(values[i]);
+
+        for (int i = 0; i < remainingValues.length; i++) {
+            current.next = new SinglyLinkedListNode(remainingValues[i]);
             current = current.next;
         }
         return head;
@@ -25,32 +22,28 @@ private static SinglyLinkedListNode listOf(int... values) {
     @Test
     void middleNodeOddLength() {
         SinglyLinkedListNode head = listOf(1, 2, 3, 4, 5);
-        SinglyLinkedListNode middle = MiddleOfLinkedList.middleNode(head);
-        assertNotNull(middle);
+        SinglyLinkedListNode middle = Objects.requireNonNull(MiddleOfLinkedList.middleNode(head));
         assertEquals(3, middle.value);
     }
 
     @Test
     void middleNodeEvenLengthReturnsSecondMiddle() {
         SinglyLinkedListNode head = listOf(1, 2, 3, 4, 5, 6);
-        SinglyLinkedListNode middle = MiddleOfLinkedList.middleNode(head);
-        assertNotNull(middle);
+        SinglyLinkedListNode middle = Objects.requireNonNull(MiddleOfLinkedList.middleNode(head));
         assertEquals(4, middle.value);
     }
 
     @Test
     void middleNodeSingleElement() {
         SinglyLinkedListNode head = listOf(42);
-        SinglyLinkedListNode middle = MiddleOfLinkedList.middleNode(head);
-        assertNotNull(middle);
+        SinglyLinkedListNode middle = Objects.requireNonNull(MiddleOfLinkedList.middleNode(head));
         assertEquals(42, middle.value);
     }
 
     @Test
     void middleNodeTwoElementsReturnsSecond() {
         SinglyLinkedListNode head = listOf(10, 20);
-        SinglyLinkedListNode middle = MiddleOfLinkedList.middleNode(head);
-        assertNotNull(middle);
+        SinglyLinkedListNode middle = Objects.requireNonNull(MiddleOfLinkedList.middleNode(head));
         assertEquals(20, middle.value);
     }
 
@@ -70,8 +63,7 @@ void middleNodeDoesNotModifyListStructure() {
         second.next = third;
         third.next = fourth;
 
-        SinglyLinkedListNode middle = MiddleOfLinkedList.middleNode(first);
-        assertNotNull(middle);
+        SinglyLinkedListNode middle = Objects.requireNonNull(MiddleOfLinkedList.middleNode(first));
         assertEquals(3, middle.value);
 
         assertEquals(second, first.next);