assertEqualCharNodes(traverser.depthFirstPreOrder(charactersOf("bd")), "bcda");
    assertEqualCharNodes(traverser.depthFirstPreOrder(charactersOf("dc")), "dabc");
    assertEqualCharNodes(traverser.depthFirstPreOrder(charactersOf("bc")), "bcda");
  }

  @Test
  public void forGraph_depthFirstPreOrder_twoCycles() {

    // These have a combination of invalid length, unrecognized characters and wrong padding.
    assertFailsToDecode(base32(), "AB=C", "Unrecognized character: =");
    assertFailsToDecode(base32(), "A=BCDE", "Invalid input length 6");
    assertFailsToDecode(base32(), "?", "Invalid input length 1");
  }

  public void testBase32UpperCaseIsNoOp() {
    assertThat(base32().upperCase()).isSameInstanceAs(base32());
  }