}

    private TestFile writeJavaSourceFile(String className) {
        String sourceFilePath = "src/main/java/${className}.java"
        sourceFilePath = prependRootDirName(sourceFilePath)
        def sourceFile = testDir.file(sourceFilePath)
        sourceFile << "public class $className {}"
        sourceFile
    }

    private TestFile determineClassFile(File sourceFile) {

     * @return the source file and it's source root
     */
    fun sourceFileAndSourceRootFor(sourceFilePath: String): Pair<File, File> =
        sourceRoots.asSequence()
            .map { it.resolve(sourceFilePath) to it }
            .firstOrNull { it.first.isFile }
            ?: throw IllegalStateException("Source file '$sourceFilePath' not found, searched in source roots:\n  - ${sourceRoots.joinToString("\n  - ")}")

    private

    TestFile file(String path) {
        projectDir.file(path)
    }

    TestFile groovy(String path) {
        file("src/main/groovy/${sourceFilePath(path)}")
    }

    TestFile java(String path) {
        file("src/main/java/${sourceFilePath(path)}")
    }

    private String sourceFilePath(String path) {
        packageName ? "${packageName.replaceAll("\\.", "/")}/$path" : path
    }

            sources.sourceFileAndSourceRootFor(declaringClass.sourceFilePath).let { (sourceFile, sourceRoot) ->
                if (declaringClass.isKotlin) ApiSourceFile.Kotlin(sourceFile, sourceRoot)
                else ApiSourceFile.Java(sourceFile, sourceRoot)
            }
        }

    private
    val JApiClass.sourceFilePath: String
        get() = if (isKotlin) kotlinSourceFilePath else javaSourceFilePath

    }

    private static void addPluginSource(TestFile pluginProjectDir, String code) {
        def packageName = "org.gradle.test"
        def sourceFilePath = "${packageName.replaceAll("\\.", "/")}/${"TestPlugin"}.groovy"
        pluginProjectDir.file("src/main/groovy/${sourceFilePath}") << """
            ${packageName ? "package $packageName" : ""}

            class TestPlugin implements $Plugin.name<$Project.name> {