Because I have tried a couple of ways, and failed... I eventually did find some documentation, http://gradle.org/current/docs/dsl/org.gradle.api.tasks.testing.Test.html
However, assuming from that, that I can go like this:
Test.workingDir = new File('/mnt/data/dev/astraia/svn/working_build')
ended in failure:
* What went wrong:
A problem occurred evaluating project ':myproject'.
Cause: No such property: workingDir for class:
org.gradle.api.tasks.testing.Test
Possible solutions: workingDir
