When I updated my Mac to Java 8, Infinitest quit working. I've been hoping it would update and start working but it didn't happen.
I went looking and I found that the Eclipse Marketplace version of Infinitest is several years old. Had the project been abandoned?
I found an Infinitest web site which linked to the Github page. The readme there gave an update site of http://update.improvingworks.com/ and when I installed/updated from that site Infinitest started working again.
The web page gives an update site of http://infinitest.github.io which appears to point to the same version (5.1.110). I'm not sure which is the "correct" choice.
Now I'm just waiting for Proguard to be updated for Java 8.