Implementing a simple Dagger2 sample

AppModule.kt: Provide the application context. No need to write @singleton @provides for your Test* classes (will see why)

@Module
class AppModule {
    @Provides
    @Singleton
    fun provideApplication(app: App): Context = app.applicationContext
}

AppComponent.kt: @Component.Builder is deprecated IIRC. Use @Component.Factory. And replace AndroidInjectionModule::class with AndroidSupportInjectionModule::class since we are using dagger-android-support and android’s *Compat* stuff. Refer a new module here called ActivityModule::class.

@Singleton
@Component(modules = [
    ActivityModule::class
    AndroidSupportInjectionModule::class,
    AppModule::class
])
interface AppComponent : AndroidInjector<App> {

    @Component.Factory
    abstract class Factory : AndroidInjector.Factory<App>
}

TestClass.kt & TestOperator.kt: Since you were providing singletons by writing @singleton and @provides method, I assume you want them to be singletons. Just annotate the class definition with @Singleton and dagger will take care of it. No need to write @Provides methods.

@Singleton
class TestClass @Inject constructor(private val testOperator: TestOperator) {
    fun getRandomValueFromCTest(): Int = testOperator.generateRandomNumber()
}

@Singleton
class TestOperator @Inject constructor() {
    fun generateRandomNumber(): Int = Random.nextInt()
}

App.kt: Using factory instead of builder since @Component.Builder is deprecated.

class App : DaggerApplication() {
    override fun applicationInjector(): AndroidInjector<out DaggerApplication> {
        return DaggerAppComponent.factory().create(this)
    }
}

ActivityModule.kt: Provide a module to dagger to create your activities.

@Module
interface ActivityModule {

    @ContributesAndroidInjector
    fun provideMainActivity(): MainActivity
}

MainActivity.kt: Finally, extend from DaggerAppCompatActivity.

class MainActivity : DaggerAppCompatActivity() {

    @Inject
    lateinit var testClass: TestClass

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
    }

    override fun onResume() {
        super.onResume()
        val x = testClass.getRandomValueFromCTest()
    }
}

I believe this should run without issues. For more reference you could look into this sample and the new simpler docs at dagger.dev/android