for (int i = 0; i < expected; i++) {
      assertTrue(permutations.hasNext());
      permutations.next();
    }
    assertNoMorePermutations(permutations);
  }

  public void testToStringImplWithNullEntries() throws Exception {
    List<@Nullable String> list = new ArrayList<>();
    list.add("foo");
    list.add(null);

    assertEquals(list.toString(), Collections2.toStringImpl(list));
  }