function testDelete_Simple() {
  var tree = insertToTree(9);
  tree.remove(3);
  var expected =
      '2[13|21]\n' +
      '_{0|1|3}_\n' +
      '0[5|9|11]  1[13|17]  3[21|25|27]\n' +
      '_{5/9/11}2  0{13/17}2  1{21/25/27}2\n';
  assertEquals(expected, tree.toString());
}
13|21
    /      |        \
3|5|9|11  13|17  21|25|27

delete 3 should just change the left most leaf node.