apply plugin: 'com.android.application'

android {
    compileSdkVersion 24
    buildToolsVersion "25.0.0"

    sourceSets {
        main {
            jniLibs.srcDirs = ['libs']
        }
    }

    defaultConfig {
        applicationId "com.lt.bottomtabdemo"
        minSdkVersion 9
        targetSdkVersion 24
        versionCode 1
        versionName "1.0"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.txt'
        }
    }
}
repositories {
    flatDir {
        dirs 'libs'
    }
}
dependencies {
    compile fileTree(include: '*.jar', dir: 'libs')
    compile 'com.android.support:support-v4:25.0.1'
    testCompile 'junit:junit:4.12'

}

默认android studio的defaultConfig节点在android节点内部，将defaultConfig节点提出来放外面，然后在android节点里面增加sourceSets节点。然后在dependencies里面增加编译代码testCompile 'junit:junit:4.12'