Isn't the real issue that there are not enough available slots for the test?
A 6 week wait initially than another 4 week wait if you were to fail is ridiculous
I doubt we'd be focused on the subject of the fail if you could book in a reasonable time (a week or two) and then be retested within the week after a fail. Than it would all be considered reasonable IMHO.
Let's not excuse a mistake just because they aren't offering enough opportunity for testing.