Add binary search tree.

src/data-structures/tree/__test__/BinaryTreeNode.test.js

@@ -0,0 +1,38 @@
+import BinaryTreeNode from '../BinaryTreeNode';
+
+describe('BinaryTreeNode', () => {
+  it('should create node', () => {
+    const node = new BinaryTreeNode();
+
+    expect(node).toBeDefined();
+
+    expect(node.value).toBeNull();
+    expect(node.left).toBeNull();
+    expect(node.right).toBeNull();
+
+    expect(node.hasLeft()).toBeFalsy();
+    expect(node.hasRight()).toBeFalsy();
+
+    const leftNode = new BinaryTreeNode(1);
+    const rightNode = new BinaryTreeNode(3);
+    const rootNode = new BinaryTreeNode(2);
+
+    rootNode
+      .addLeft(leftNode)
+      .addRight(rightNode);
+
+    expect(rootNode.value).toBe(2);
+    expect(rootNode.left.value).toBe(1);
+    expect(rootNode.right.value).toBe(3);
+  });
+
+  it('should traverse node', () => {
+    const leftNode = new BinaryTreeNode(1);
+    const rightNode = new BinaryTreeNode(3);
+    const rootNode = new BinaryTreeNode(2, leftNode, rightNode);
+
+    expect(rootNode.traverseInOrder()).toEqual([null, 1, null, 2, null, 3, null]);
+
+    expect(rootNode.toString()).toBe('1,2,3');
+  });
+});