The jtreg plugins calls some methods from the ant plugin configuration classes. In the newest version of the ant plugin, one of these methods has been removed:

https://github.com/JetBrains/intellij-community/commit/265fee5a6e051d9d8f49403d48c5694a557e522c

This causes the jtreg plugin to crash with a NoSuchMethodError, and running tests is no longer possible.