Create getters and setters for meta data in binary tree node.

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

@@ -204,4 +204,23 @@ describe('BinaryTreeNode', () => {
     expect(redNode.meta.color).toBe('red');
     expect(blackNode.meta.color).toBe('black');
   });
+
+  it('should be possible to use get/set methods to change node meta information', () => {
+    const redNode = new BinaryTreeNode(1, { color: 'red' });
+    const blackNode = new BinaryTreeNode(2, { color: 'black' });
+
+    expect(redNode.getMeta('color')).toBe('red');
+    expect(blackNode.getMeta('color')).toBe('black');
+
+    redNode.setMeta('size', 8);
+
+    expect(redNode.getMeta('size')).toBe(8);
+    expect(redNode.getMeta('color')).toBe('red');
+    expect(redNode.getMeta('not_existing')).toBeNull();
+
+    // It must also be possible to override meta information.
+    redNode.setMeta('color', 'blue');
+    expect(redNode.getMeta('size')).toBe(8);
+    expect(redNode.getMeta('color')).toBe('blue');
+  });
 });