testMinAndMaxValues() {
    const tree = new AvlTree((a, b) => a - b);

    const NUM_TO_INSERT = 2000;
    const NUM_TO_REMOVE = 500;

    // Insert ints into tree out of order
    for (let i = 0; i < NUM_TO_INSERT; i += 1) {
      tree.add(i);
    }

    // Remove valuse
    for (let i = 0; i < NUM_TO_REMOVE; i += 1) {
      tree.remove(i);
    }

    assertEquals(tree.getMinimum(), NUM_TO_REMOVE);
    assertEquals(tree.getMaximum(), NUM_TO_INSERT - 1);
  }
This test verifies that we can insert values into and remove values from
the AvlTree and have its minValue and maxValue routines return the correct
min and max values contained by the tree.