The testPlayBinary task does not include resources from the test/resources directory, which is the default test resources directory when building play applications using SBT.
I’ve modified PlayTestPlugin to add a task that copies the resources into the test classpath. The pull request is #527 (sorry, unable to post a link)
I think ultimately the resource path should be exposed and configurable via the DSL, but this should be a good workaround for the present.