test: write test cases for singly LinkedList class

Author: francislagares

src/linked-list/LinkedList.ts

@@ -7,18 +7,18 @@ export class Node<T> implements INode<T> {
   public data: T;
   public next?: INode<T>;
 
-  constructor(data: T) {
+  constructor(data?: T) {
     this.data = data;
     this.next = null;
   }
 }
 
 export class LinkedList<T> {
-  private head: INode<T> | null;
-  protected tail: INode<T> | null;
+  public head: INode<T> | null;
+  public tail: INode<T> | null;
   protected length: number;
 
-  constructor(data: T) {
+  constructor(data?: T) {
     this.head = new Node(data);
     this.tail = this.head;
     this.length = 1;

src/linked-list/__tests__/LinkedList.test.ts

@@ -0,0 +1,57 @@
+import { LinkedList, Node } from '../LinkedList';
+
+describe('Singly Linked List', () => {
+  test('create empty list node', () => {
+    const node = new Node();
+
+    expect(node.data).toBeUndefined();
+    expect(node.next).toBeNull();
+  });
+
+  test('create list node with value', () => {
+    const node = new Node(10);
+
+    expect(node.data).toBe(10);
+    expect(node.next).toBeNull();
+  });
+
+  test('create list node with object as a value', () => {
+    const nodeValue = { key: 1, value: 'test' };
+    const node = new Node(nodeValue);
+
+    expect(node.data.key).toBe(1);
+    expect(node.data.value).toBe('test');
+    expect(node.next).toBeNull();
+  });
+
+  test('append node to linked list', () => {
+    const linkedList = new LinkedList();
+
+    linkedList.append(5);
+
+    expect(linkedList.head.data).toBeUndefined();
+    expect(linkedList.head.next.data).toBe(5);
+    expect(linkedList.head.next.next).toBeNull();
+  });
+
+  test('prepend node to linked list', () => {
+    const linkedList = new LinkedList();
+
+    linkedList.prepend(5);
+
+    expect(linkedList.head.data).toBe(5);
+    expect(linkedList.tail.next).toBeNull();
+  });
+
+  test('insert node list in a given index', () => {
+    const linkedList = new LinkedList();
+
+    const nodeValue1 = { value: 1, key: 'key1' };
+    const nodeValue2 = { value: 2, key: 'key2' };
+    const nodeValue3 = { value: 3, key: 'key3' };
+
+    linkedList.append(nodeValue1).prepend(nodeValue3).insert(1, nodeValue2);
+
+    expect(linkedList.head.next.data).toEqual({ value: 2, key: 'key2' });
+  });
+});