* Data#members might not be defined, instead it might be defined
  on Data subclasses or a module included there. This is notably the
  case on TruffleRuby which defines it there for optimization purposes.
  In fact the mere presence of Data#members implies a megamorphic call
  inside, so it seems best to avoid relying on its existence.

…nymous

* It would be "#<data  a=42>" (double space) instead of "#<data a=42>" (like #inspect).

* Only 2 cyclic tests are failing, with the ... in a slightly different place in the output.