Add more test cases for linked list reversion.

Author: trekhleb

src/data-structures/linked-list/LinkedList.js

@@ -243,27 +243,27 @@ export default class LinkedList {
   }
 
   /**
-   * Reverse a singly linked list use to three variables
-   * @returns {ReservedLinkedList}
+   * Reverse a linked list.
+   * @returns {LinkedList}
    */
   reverse() {
     let currNode = this.head;
     let prevNode = null;
     let nextNode = null;
 
     while (currNode) {
-      // Store next node
+      // Store next node.
       nextNode = currNode.next;
 
-      // Change next node of the current
+      // Change next node of the current node so it would link to previous node.
       currNode.next = prevNode;
 
-      // Move forward prev and current nodes one step
+      // Move prevNode and currNode nodes one step forward.
       prevNode = currNode;
       currNode = nextNode;
     }
 
-    // Reset head, tail
+    // Reset head and tail.
     this.tail = this.head;
     this.head = prevNode;
 

src/data-structures/linked-list/__test__/LinkedList.test.js

@@ -243,15 +243,24 @@ describe('LinkedList', () => {
     expect(() => linkedList.reverseTraversal(linkedList.head)).toThrow();
   });
 
-  it('should reverse the singly linked list', () => {
+  it('should reverse linked list', () => {
     const linkedList = new LinkedList();
 
+    // Add test values to linked list.
     linkedList
       .append(1)
       .append(2)
       .append(3);
 
     expect(linkedList.toString()).toBe('1,2,3');
-    expect(linkedList.reverse().toString()).toBe('3,2,1');
+    expect(linkedList.head.value).toBe(1);
+    expect(linkedList.tail.value).toBe(3);
+
+    // Reverse linked list.
+    linkedList.reverse();
+
+    expect(linkedList.toString()).toBe('3,2,1');
+    expect(linkedList.head.value).toBe(3);
+    expect(linkedList.tail.value).toBe(1);
   });
 });