IMHO Spock is the best test framework out there.
However currently it is not supported well in IDEA.
There are so many issues open related to Spock, see YouTrack
Especially bad are all those false warnings, because we would like to "keep our code clean" and always getting false warning in IDEA makes developers get used to having warnings and ignoring them elsewhere, too.
For example IDEA-171181, IDEA-182592, IDEA-127650, IDEA-121812