set("a", "a1", "a2")
    val iterator = cache.snapshots()
    assertFailsWith<IllegalStateException> {
      iterator.remove()
    }
  }

  @Test
  fun iteratorRemoveOncePerCallToNext() {
    set("a", "a1", "a2")
    val iterator = cache.snapshots()
    iterator.next().use {
      iterator.remove()
    }
    assertFailsWith<IllegalStateException> {
      iterator.remove()