I’m creating this issue to bring attention to the issue I posted a month ago: TestNG parallel test execution hangs up. No reaction during the last month.
I tested it against Gradle 2.11 and Gradle 2.12-rc-1 and got same results.
Have a look at https://issues.gradle.org/browse/GRADLE-3189, probably you are observing this issue. We faced it on our project and it prevents us from moving our tests execution from maven to gradle.