If you set up your project with the default gradle package structure, i.e.:
src/main/java
src/main/resources
src/test/java
src/test/resources
then you won't need to modify sourceSets to run your tests. Gradle will figure out that your test classes and resources are in src/test. You can then run as Oliver says above. One thing to note: Be careful when setting property files and running your test classes with both gradle and you IDE. I use Eclipse, and when running JUnit from it, Eclipse chooses one classpath (the bin directory) whereas gradle chooses another (the build directory). This can lead to confusion if you edit a resource file, and don't see your change reflected at test runtime.