If you add that ability to Proof, you can test with the ancients and still get 100% coverage of the promise additions by writing the tests so that they return a Thenable instead of a Promise.
How would we go about testing with the ancients, though? Proof is no longer tested against pre-async/await Node.js because one of its dependencies uses a static ES6 declaration. We'd have to revert changes.
If you add that ability to Proof, you can test with the ancients and still get 100% coverage of the promise additions by writing the tests so that they return a
Thenable
instead of aPromise
.