public void ReturnValueUsingBfsSearch()
        {
            var root = new TreeNode <char>('a');
            var b    = new TreeNode <char>('b');
            var c    = new TreeNode <char>('c');
            var d    = new TreeNode <char>('d');
            var e    = new TreeNode <char>('e');
            var f    = new TreeNode <char>('f');

            root.Left  = b;
            root.Right = c;
            b.Right    = e;
            b.Left     = d;
            c.Right    = f;

            //      a
            //     / \
            //    b    c
            //   / \    \
            //  d   e    f

            var expected = new List <char>()
            {
                'a', 'b', 'c', 'd', 'e', 'f'
            };

            var result = _sut.BfsTraverse(root);

            CollectionAssert.AreEqual(expected, result);
        }