Three little words in the 102-page protocol that China signed when it agreed to join the World Trade Organization is turning into a litmus test for the institution itself: non-market economy.

One year ago today was the 15th anniversary of China joining the WTO. The date is important because of a little clause in the accession protocols that deals with how countries should decide whether the goods that China exports have been unfairly dumped. It says: “In any event, the provisions [that allow trade disputants to treat China as a non-market economy] shall expire 15 years after the date of accession”.

In the year following that expiry date, a battle royale has erupted over whether Europe and the US should honour what Beijing sees as its agreement when the other countries say China has not stood by its commitments.