Android : Android Unit testing using gradle

I want to do unit testing using gradle with out using any device or emulator, below is my code. Its not working, getting error like Could not find property 'output' on source set unit test can anybody suggest me how to resolve this.

buildscript {

 repositories {
   mavenCentral()
 }

  dependencies {
   classpath 'com.android.tools.build:gradle:0.11+'
  }
}

apply plugin: 'android'

android {
   compileSdkVersion 19
   buildToolsVersion '19.1'

   sourceSets {
     main {
           manifest.srcFile 'AndroidManifest.xml'
           java.srcDirs = ['src']
           resources.srcDirs = ['src']
           renderscript.srcDirs = ['src']
           res.srcDirs = ['res']
           assets.srcDirs = ['assets']
          }
   }

   dependencies {
     compile files('libs/android-support-v4.jar')
   }

   lintOptions {
      abortOnError true
      textReport true
      textOutput 'stdout'
   }

   sourceSets {
       unitTest {
           java.srcDir file('src/test')
   }
 }

 configurations {
      unitTestCompile.extendsFrom runtime
      unitTestRuntime.extendsFrom unitTestCompile
 }
 dependencies {
      unitTestCompile files("$project.buildDir/classes/release")
      unitTestCompile 'junit:junit:4.8.2'
 }
 task unitTest(type:Test, dependsOn: assemble) {
      description = "run unit tests"
      testClassesDir = android.sourceSets.unitTest.output.classesDir
      classpath = android.sourceSets.unitTest.runtimeClasspath
 }

 check.dependsOn unitTest


}