assertWithMessage("Expected to return non-null for: %s", mutableClass)
          .that(instance)
          .isNotNull();
      assertNotSame(
          "Expected to return fresh instance for: " + mutableClass,
          instance,
          ArbitraryInstances.get(mutableClass));
    }
  }

  private enum EmptyEnum {}

  private enum Direction {
    UP,
    DOWN
  }

      assertWithMessage("Expected to return non-null for: %s", mutableClass)
          .that(instance)
          .isNotNull();
      assertNotSame(
          "Expected to return fresh instance for: " + mutableClass,
          instance,
          ArbitraryInstances.get(mutableClass));
    }
  }

  private enum EmptyEnum {}

  private enum Direction {
    UP,
    DOWN
  }