@bmuschko Classpath ordering seems to matter for TestKit in 2.13, causing this kind of error in IntelliJ. Same test succeeds on the command line.
java.lang.NoSuchMethodError: org.gradle.tooling.internal.consumer.DefaultBuildLauncher.withInjectedClassPath(Lorg/gradle/testkit/jarjar/org/gradle/internal/classpath/ClassPath;)Lorg/gradle/tooling/internal/consumer/AbstractLongRunningOperation;
at org.gradle.testkit.runner.internal.ToolingApiGradleExecutor.run(ToolingApiGradleExecutor.java:98)
at org.gradle.testkit.runner.internal.DefaultGradleRunner.run(DefaultGradleRunner.java:270)
at org.gradle.testkit.runner.internal.DefaultGradleRunner.build(DefaultGradleRunner.java:219)
You should be able to reproduce by importing the gradle-2.13 branch of gradle-lint into IntelliJ. The failing test is UnusedDependencyRuleSpec.