Have you gone through this documentation?
You need to add some of these dependencies based on your need.
dependencies {
androidTestCompile 'com.android.support.test:runner:0.4'
// Set this dependency to use JUnit 4 rules
androidTestCompile 'com.android.support.test:rules:0.4'
// Set this dependency to build and run Espresso tests
androidTestCompile 'com.android.support.test.espresso:espresso-core:2.2.1'
// Set this dependency to build and run UI Automator tests
androidTestCompile 'com.android.support.test.uiautomator:uiautomator-v18:2.1.2'
}
And add :
android {
defaultConfig {
testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
}
}