Arcane Laboratory

• WWizards of the Coast2004-10-04
  Official Ruling
  When it leaves the battlefield, the effect ends and all players are able to cast spells unrestricted again.
• WWizards of the Coast2004-10-04
  Official Ruling
  When Arcane Laboratory enters, it will look back over the turn to see if any spell was cast before it entered the battlefield. It will notice itself being cast.
• WWizards of the Coast2004-10-04
  Official Ruling
  If a spell is countered, it still counts as the one spell cast.

Rulings via Scryfall