Harry was tested (via Veritaserum) after the Daily Prophet incident. The fact that he is being tested in regards to Quirrell's illegal activity is not evidence of it's failure, it only shows that it's impossible enough to make someone suspect Harry Potter was involved.
A flashback where Quirrell explains the failsafe to Harry might have helped, though. For example, he would have foresaw the hide-from-dementors nature of Patronus 2.0 as a clue for Dumbledore (which is probably what prompted him to make this particular failsafe in the first place). How much of it did he explain to Harry?
It is not really important, however. The moment Harry recieved the message at 3PM, he was committed. DO NOT MESS WITH TIME!
Still, your question made me notice my (possible) confusion, so... good one.
The alarming thing about being tested isn't that they tested Harry specifically; it is that they were aware that tests needed to be performed at all. Had the plan gone successfully, nobody would have ever have known that Bellatrix was removed. Remember that the entire advantage of Patronus 2.0 (to Quirrell) was the undetectable nature of it. It allowed a person to commit a perfect crime without the guards or dementors being aware that a crime ever occurred.
From the point of view of Harry, sitting with his invisibility cloak in the empty room at 3:00 PM,...
Update: Discussion has moved on to a new thread.
The load more comments links are getting annoying (at least if you're not logged in), so it's time for a new Harry Potter and the Methods of Rationality discussion thread. We're also approaching the traditional 500-comment mark, but I think that hidden comments provide more appropriate joints to carve these threads at. So as of chapter 67, this is the place to share your thoughts about Eliezer Yudkowsky's Harry Potter fanfic.
The first 5 discussion threads are on the main page under the harry_potter tag. Threads 6 and on (including this one) are in the discussion section using its separate tag system. Also: one, two, three, four, five, six. The fanfiction.net author page is the central author-controlled HPMOR clearinghouse with links to the RSS feed, pdf version, TV Tropes pages, fan art, and more, and AdeleneDawner has kept an archive of Author's Notes.
As a reminder, it's often useful to start your comment by indicating which chapter you are commenting on.
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: