creator.setString(1, "DE")
    creator.commit()
    cache.flush()
    filesystem.copy(journalFile, journalBkpFile)
    creator = cache.edit("k2")!!
    creator.setString(0, "F")
    creator.setString(1, "GH")
    creator.commit()
    cache.close()
    assertThat(filesystem.exists(journalFile)).isTrue()
    assertThat(filesystem.exists(journalBkpFile)).isTrue()
    createNewCache()
    val snapshotA = cache["k1"]!!

   *   b   e   g
   *  / \ / \ /
   * c   d   h
   * }
   */
  private static final SuccessorsFunction<Character> GRAPH_CONTAINING_TREE_AND_DIAMOND =
      createDirectedGraph("ab", "fe", "fg", "bc", "bd", "ed", "eh", "gh");

  @Test
  public void forGraph_breadthFirst_javadocExample_canBeIteratedMultipleTimes() {
    Iterable<Character> result = Traverser.forGraph(JAVADOC_GRAPH).breadthFirst('a');