Add jest tests.

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

@@ -0,0 +1,49 @@
+import Node from './Node';
+
+export default class LinkedList {
+  constructor() {
+    this.head = null;
+  }
+
+  append(value) {
+    const newNode = new Node(value);
+
+    // If there is no head yet let's make new node a head.
+    if (!this.head) {
+      this.head = newNode;
+
+      return newNode;
+    }
+
+    // Rewind to last node.
+    let currentNode = this.head;
+    while (currentNode.next !== null) {
+      currentNode = currentNode.next;
+    }
+
+    // Attach new node to the end of linked list.
+    currentNode.next = newNode;
+
+    return newNode;
+  }
+
+  prepend(value) {
+    this.head = new Node(value, this.head);
+  }
+
+  toArray() {
+    const listArray = [];
+    let currentNode = this.head;
+
+    while (currentNode) {
+      listArray.push(currentNode.value);
+      currentNode = currentNode.next;
+    }
+
+    return listArray;
+  }
+
+  toString() {
+    return this.toArray().toString();
+  }
+}

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

@@ -0,0 +1,6 @@
+export default class Node {
+  constructor(value, next = null) {
+    this.value = value;
+    this.next = next;
+  }
+}

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

@@ -0,0 +1,23 @@
+import LinkedList from '../LinkedList';
+
+describe('LinkedList', () => {
+  it('should create empty linked list', () => {
+    const linkedList = new LinkedList();
+    expect(linkedList).toBeDefined();
+  });
+
+  it('should append node to linked list', () => {
+    const linkedList = new LinkedList();
+    linkedList.append(1);
+    linkedList.append(2);
+    expect(linkedList.toString()).toBe('1,2');
+  });
+
+  it('should prepend node to linked list', () => {
+    const linkedList = new LinkedList();
+    linkedList.append(1);
+    linkedList.append(2);
+    linkedList.prepend(3);
+    expect(linkedList.toString()).toBe('3,1,2');
+  });
+});

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

@@ -0,0 +1,9 @@
+import Node from '../Node';
+
+describe('Node', () => {
+  it('should create list node with value', () => {
+    const node = new Node(1);
+    expect(node.value).toBe(1);
+    expect(node.next).toBeNull();
+  });
+});