问Junit 4不识别测试

EN

apply plugin: 'com.android.application'

android {
    compileSdkVersion 23
    buildToolsVersion "23.0.3"

    defaultConfig {
        testApplicationId "com.commonsware.android.retrofit.test"
    }
}

dependencies {
    compile 'com.squareup.retrofit:retrofit:1.6.1'
    compile 'de.greenrobot:eventbus:2.2.1'
    testCompile 'junit:junit:4.12'
    androidTestCompile 'com.android.support.test:rules:0.4.1'
}

package com.commonsware.android.retrofit;

/**
 * To work on unit tests, switch the Test Artifact in the Build Variants view.
 */
public class ExampleUnitTest {
    @Test
    public void addition_isCorrect() throws Exception {
        assertEquals(4, 2 + 2);
    }
}