✅ If the value of the internal slot [[completeCalled]] is true, reject promise with an "InvalidStateError" DOMException.
✅ Passing no argument defaults to "unknown", eventually closing the sheet and doesn't throw.
✅ Passing "success" eventually closes the sheet and doesn't throw.
✅ Passing "fail" eventually closes the sheet and doesn't throw.

PASS Can construct a payment request (smoke test). 
PASS If the value of the internal slot [[completeCalled]] is true,
      reject promise with an "InvalidStateError" DOMException. 
PASS Passing no argument defaults to "unknown",
      eventually closing the sheet and doesn't throw. 
PASS Passing "success" eventually closes the sheet and doesn't throw. 
PASS Passing "fail" eventually closes the sheet and doesn't throw.