--update : add doublyLinkedList test

Author: TheSTL

src/_DataStructures_/DoublyLinkedList/doublyLinkedList.test.js

@@ -0,0 +1,40 @@
+const DLL = require('.');
+
+describe('Doubly Linked List', () => {
+  const doublyLinkedList = new DLL();
+
+  it('create DLL', () => {
+    expect(doublyLinkedList.head.next).toEqual(doublyLinkedList.tail);
+    expect(doublyLinkedList.tail.previous).toEqual(doublyLinkedList.head);
+    expect(doublyLinkedList.length()).toEqual(0);
+  });
+
+  it('addAtBeginning', () => {
+    doublyLinkedList.addAtBeginning(1);
+    doublyLinkedList.addAtBeginning(2);
+    doublyLinkedList.addAtBeginning(3);
+    expect(doublyLinkedList.traverse()).toEqual([3, 2, 1]);
+  });
+
+  it('addAtEnd', () => {
+    doublyLinkedList.addAtEnd(1);
+    doublyLinkedList.addAtEnd(2);
+    doublyLinkedList.addAtEnd(3);
+    expect(doublyLinkedList.traverse()).toEqual([3, 2, 1, 1, 2, 3]);
+  });
+
+  it('removeAtBeginning', () => {
+    doublyLinkedList.removeAtBeginning();
+    doublyLinkedList.removeAtBeginning();
+    doublyLinkedList.removeAtBeginning();    
+    expect(doublyLinkedList.traverse()).toEqual([1, 2, 3]);
+  });
+
+  it('removeAtEnd', () => {
+    doublyLinkedList.removeAtEnd();
+    doublyLinkedList.removeAtEnd();
+    doublyLinkedList.removeAtEnd();
+
+    expect(doublyLinkedList.traverse()).toEqual([]);
+  });
+});