Spock is a framework used to write tests using the Groovy language and its adoption has been increasing lately. Although Groovy is the language you must use to write your tests with Spcok, it can be used for both Groovy and Java applications and is compatible with most of the Java IDEs, including Eclipse.
The idea of writing the tests using Groovy can be seen as an obstacle for some Java developers that are not familiar with Groovy. However, the knowledge required in Groovy is quite basic and the Spock documentation itself is very helpful with this question. I myself, right now, know very little about Groovy and this hasn’t been an issue to write tests with Spock.