assertEqualCharNodes(traverser.breadthFirst(charactersOf("db")), "db");
  }

  @Test
  public void forGraph_breadthFirst_multiGraph() {
    Traverser<Character> traverser = Traverser.forGraph(MULTI_GRAPH);
    assertEqualCharNodes(traverser.breadthFirst('a'), "abcd");
    assertEqualCharNodes(traverser.breadthFirst('b'), "bd");

  public void testFileTraverser_emptyDirectory() throws Exception {
    assertThat(Files.fileTraverser().breadthFirst(rootDir)).containsExactly(rootDir);
  }

  public void testFileTraverser_nonExistingFile() throws Exception {
    File file = new File(rootDir, "file-that-doesnt-exist");

    assertThat(Files.fileTraverser().breadthFirst(file)).containsExactly(file);
  }

  public void testFileTraverser_file() throws Exception {