Task dependencies are not currently being exercised when testing via ProjectBuilder created Project instances. See http://j.mp/aaZBTk for more information.

Per Adam's response in that thread:

We're certainly missing some testing support at the higher levels. Perhaps something like:

• A fixture at the same level as GradleLauncher, for writing integration tests at the command-line level. At this level, the test sets up a test build on the file system, runs the build, and then makes some assertions about what happened.
• Something between that and ProjectBuilder, where the test sets up the model programmatically, runs a task (and implicitly its dependencies), and then makes some assertions about what happened.