/** Checks idempotency, and that we observe the promised number of stripes. */
  public void testBasicInvariants() {
    for (Striped<?> striped : allImplementations()) {
      assertBasicInvariants(striped);
    }
  }

  private static void assertBasicInvariants(Striped<?> striped) {
    Set<Object> observed = Sets.newIdentityHashSet(); // for the sake of weakly referenced locks.
    // this gets the stripes with #getAt(index)

  /** Checks idempotency, and that we observe the promised number of stripes. */
  public void testBasicInvariants() {
    for (Striped<?> striped : allImplementations()) {
      assertBasicInvariants(striped);
    }
  }

  private static void assertBasicInvariants(Striped<?> striped) {
    Set<Object> observed = Sets.newIdentityHashSet(); // for the sake of weakly referenced locks.
    // this gets the stripes with #getAt(index)