So much so, that there have been some who have glossed over the fact that just two of Arsenal's wins this season have come against clubs that could be considered equals.
Those earlier tests, against teams in transition in the shape of Tottenham Hotspur and Napoli, had been overcome rather than passed with flying colours and there was always the suspicion that the true measure of Arsene Wenger's side had yet to be taken.
It was done so here by Borussia Dortmund. A side that came within a whisker of lifting the Champions League trophy last season may have required a late Robert Lewandowski winner but they did so when the match appeared destined for a draw.
In the process of executing his winner, the Pole raised questions about Arsenal's resolve, queries that were made all the more pertinent by Napoli's 2-1 victory in Marseille, a result that has made the qualification picture in Group F just that little bit muddier.
"It's going to be tough," said Mikel Arteta, the Arsenal captain. "We knew that it was probably the toughest group in the Champions League, we don't think any different now. We are still capable of going through but we are disappointed to lose the game."
Dortmund had looked lively from kick-off, with Marco Reus supporting Lewandowski as the manager Jurgen Klopp watched on from the stands as he serves his UEFA touchline ban.
The Barclays Premier League leaders had done well to recover from the setback of falling behind to Henrikh Mkhitaryan's drilled opener in the 16th minute after Lewwandowski had seized on Aaron Ramsey's mistake on the edge of his own area to play in the Armenian.
Olivier Giroud's close-range strike sent the teams into the break on level terms, before the substitute Santi Cazorla sent a 20-yard effort against the woodwork.
However, all of their efforts were undone as the German side netted with just eight minutes remaining on the counter-attack when Lewandowski swept home to ruin Arsene Wenger's 64th birthday and leave the Londoners with plenty of work to do if they are to qualify for the knockout stages. Arteta preferred to concentrate on the postives of Arsenal's performance rather than the significance of the result.
"I think we played some really good stuff and we were unlucky to concede the goal when I thought we were playing the better football," he said. "We did the hardest bit to score just before half-time and I thought that we had control of the game and were creating the better chances, we just got caught on the counter attack.
"I think we kept them really quiet but obviously they got that chance and they scored."