Trying to create a uber.jar build file for a Gradle multi-project build

build.gradle.java

apply plugin: 'java'
group = 'qa.webdriver'

subprojects {

    apply plugin: 'java'
    
    project.ext.sourceCompatibility = 1.6
    
    repositories {
        mavenCentral()
        maven {
            url "http://maven2.javacpp.googlecode.com/git/"
        }
        maven {
            url "http://maven2.javacv.googlecode.com/git/"
        }
    }
    
    dependencies {
        compile group: 'org.sikuli', name: 'sikuli-api', version: '1.0.+'
        compile group: 'org.seleniumhq.selenium', name: 'selenium-java', version: '2.+'
        compile group: 'junit', name: 'junit', version: '4.+'
        compile group: 'org.slf4j', name: 'slf4j-api', version: '1.7.+'
        compile group: 'ch.qos.logback', name: 'logback-core', version: '1.0.+'
        compile group: 'ch.qos.logback', name: 'logback-classic', version: '1.0.+'
    }

    test {
    
        testLogging {
            exceptionFormat "full"
            events "started", "passed", "skipped", "failed", "standardOut", "standardError"
        }
          
    }
    
    // move this task to the sub project build file because of the Main-Class value
    task testJar(type: Jar) {
        classifier = 'tests'
        from sourceSets.test.output.classesDir
        manifest { attributes 'Main-Class': 'qa.webdriver.tests.GoogleTest' }
    }
    
}

subprojects.each { subproject -> evaluationDependsOn( subproject.path ) }

task uberJar(type: Jar, dependsOn: subprojects.tasks['testClasses'] ) {
    baseName = 'uberJar'
    subprojects.each { subproject ->
        from subproject.configurations.archives.allArtifacts.files.collect {
            zipTree(it)
        }
        from files(subproject.tasks["test"].testClassesDir)
        from configurations.compile.collect { it.isDirectory() ? it : zipTree(it) }
    }

}

artifacts {
    archives uberJar
}