The individual test cases in payment-request/updateWith-method-pmi-handling-manual.https.html seem to pass all test assertions, but still end up with a test harness error due to an unhandledrejection event firing.

I can't figure out where the unhandled rejection comes from. All of these tests call PaymentRequestUpdateEvent.updateWith(invalidDetails), where invalidDetails contains an invalid payment method identifier. This causes the update to be aborted with a RangeError and rejects request.[[showPromise]], both are expected according to the spec. The test verifies this rejection with await promise_rejects(t, new RangeError(), showPromise);. What's strange is that the test report shows a pass for the test but with a harness error:

Harness status: Error

Failed to construct 'PaymentDetailsUpdate': Invalid payment method identifier format
undefined:undefined:undefined

It's also weird that the last test case on the page doesn't exhibit this behavior. The only difference between it and the others is that it calls done() right after the test method (here). I wonder if this is a race condition between done() and the unhandledrejection event handler triggering.

Because of this problem, the test page has to be reloaded after each test case. I'd like to fix it, but need help figuring out where the unhandled rejection comes from.

@marcoscaceres any ideas?