There is a mistake in DSL Reference (Gradle 2.2.1): http://www.gradle.org/docs/current/dsl/org.gradle.api.Project.html
testReportDirName The name of the test reports directory. Can be a name or a path relative to the build dir.
Not true, testReportDirName is relative to reportsDir property.
Also reportsDir property is not listed in properties list of this DSL Reference.