I also agree with this analysis, and I will take it a step further. Not only did he want to test Pentangeli's reaction, he wanted Pentangeli, who was already uneasy that Michael came unnanounced, to be so shaken that he would give up on his idea to wipe out the Rosatos and make a deal with them as part of a larger plan to help Michael take his revenge against Roth.
That was
exactly his purpose. Frankie was so shaken by Michael's unannounced appearance, and so grateful that Michael didn't blame him for the Tahoe attempt, that he agreed to take a huge risk by meeting with the Rosatos. It was a win/win for Michael: If Frankie and the Rosatos settled their differences, it was one more detail he didn't have to worry about. If they tried to whack Frankie, it was one more proof that Roth was behind the Tahoe shooting. Although Michael didn't need more proof at that point, it was more icing on the cake.
It was Michael at his most manipulative and, IMO, Pacino's best scene in II.
