AndroidStudio Robolectric Unit Tests - Invaild default

I want to use Unit Testsfor my Android Application. First, I've tried the Unit-Tests with Robolectric with a template Project "deckard-gradle-master". As it worked fine, I wanted to integrate this testing in my existing Android Application. I have added the libraries hamcrest-core-1.3.jar, junit-4.12.jar, robolectric-2.4.jar and robolectric-gradle-plugin-1.0.1.jar. When i try to start my TestClass in this Project, I always get the following Exception:

Exception in thread "main" java.lang.annotation.AnnotationFormatError: Invalid default: public abstract java.lang.Class org.robolectric.annotation.Config.application()
at java.lang.reflect.Method.getDefaultValue(Method.java:611)
at sun.reflect.annotation.AnnotationType.<init>(AnnotationType.java:128)
at sun.reflect.annotation.AnnotationType.getInstance(AnnotationType.java:85)
at sun.reflect.annotation.AnnotationParser.parseAnnotation2(AnnotationParser.java:266)
at sun.reflect.annotation.AnnotationParser.parseAnnotations2(AnnotationParser.java:120)
at sun.reflect.annotation.AnnotationParser.parseAnnotations(AnnotationParser.java:72)
at java.lang.Class.createAnnotationData(Class.java:3521)
at java.lang.Class.annotationData(Class.java:3510)
at java.lang.Class.getAnnotation(Class.java:3415)
at com.intellij.junit4.JUnit4TestRunnerUtil.buildRequest(JUnit4TestRunnerUtil.java:199)
at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:39)
at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:211)
at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:67)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:134)
Process finished with exit code 1

I really don't know what to do anymore, but i think something is missing. Unfortunately i don't know what.

These are my gradle-files:

// Top-level build file where you can add configuration options common to all sub-projects/modules.

    buildscript {
        repositories {
            jcenter()
        }
        dependencies {
            classpath 'com.android.tools.build:gradle:1.1.0'
            classpath 'org.robolectric:robolectric-gradle-plugin:1.0.1'

            // NOTE: Do not place your application dependencies here; they belong
            // in the individual module build.gradle files
        }
        }

        allprojects {
         repositories {
            jcenter()
        }
        }

and

apply plugin: 'com.android.application'

android {
    compileSdkVersion 21
    buildToolsVersion "21.1.2"

    defaultConfig {
        applicationId "com.example.bieren.myapplication"
        minSdkVersion 19
        targetSdkVersion 21
        versionCode 1
        versionName "1.0"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

    dependencies {
        compile fileTree(include: ['*.jar'], dir: 'libs')
        compile 'com.android.support:appcompat-v7:21.0.3'
        compile files('libs/junit-4.12.jar')
        compile files('libs/robolectric-2.4.jar')
        compile files('libs/robolectric-annotations-2.4.jar')
        compile files('libs/hamcrest-core-1.3.jar')
        compile files('libs/android.jar')
        compile files('libs/android-libcore-4.3_r2.robolectric-0.jar')
        compile files('libs/robolectric-2.4-jar-with-dependencies.jar')
        compile files('libs/android-support-v4.jar')
        compile files('libs/maps.jar')
        androidTestCompile 'org.hamcrest:hamcrest-integration:1.1'
        androidTestCompile 'org.hamcrest:hamcrest-core:1.1'
        androidTestCompile 'org.hamcrest:hamcrest-library:1.1'
        androidTestCompile('junit:junit:4.+') {
            exclude module: 'hamcrest-core'
        }
        androidTestCompile('org.robolectric:robolectric:2.3') {
            exclude module: 'classworlds'
            exclude module: 'commons-logging'
            exclude module: 'httpclient'
            exclude module: 'maven-artifact'
            exclude module: 'maven-artifact-manager'
            exclude module: 'maven-error-diagnostics'
            exclude module: 'maven-model'
            exclude module: 'maven-project'
            exclude module: 'maven-settings'
            exclude module: 'plexus-container-default'
            exclude module: 'plexus-interpolation'
            exclude module: 'plexus-utils'
            exclude module: 'support-v4'
            exclude module: 'wagon-file'
            exclude module: 'wagon-http-lightweight'
            exclude module: 'wagon-provider-api'
        }
        compile files('libs/robolectric-gradle-plugin-1.0.1.jar')
    }

This is my Testclass:

package com.example.bieren.testapplication.test;

import android.content.Intent;
import android.os.Bundle;
import android.widget.Button;
import android.widget.TextView;

import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.robolectric.Robolectric;
import org.robolectric.RobolectricTestRunner;
import org.robolectric.annotation.Config;

import static org.hamcrest.core.IsEqual.equalTo;
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertThat;
import static org.junit.Assert.assertTrue;

@RunWith(RobolectricTestRunner.class)
@Config(manifest = "src/main/AndroidManifest.xml", emulateSdk = 18)
public class MainActivityTest {

    private MainActivity activity;

    @Test
    public void testIcon() throws Exception {
        String play_icon = new MainActivity().getResources().getString(R.string.icon_play);
        assertThat(play_icon, equalTo(""));
    }
    @Before
    public void setup(){
        this.activity = Robolectric.buildActivity(MainActivity.class).create().get();
    }
    @Test
    public void buttonClickShouldSetText() throws Exception
    {
        Button button = (Button) activity.findViewById(R.id.button);
        TextView textView = (TextView) activity.findViewById(R.id.nachricht);
        textView.setText("Hans Hans");
        button.performClick();

        assertEquals(textView.getText(),"Hans Hans");
    }

}

I would really be more than thankful if someone could tell me whats the problem and what's missing.

Timon