Unit testing. java.lang.NullPointerException - android-studio

Question

everyone! I am writing unit tests for the mobile app. But I have an error that I don't know how to solve. The error has the following form:
java.lang.NullPointerException
at androidx.appcompat.app.AppCompatDelegateImpl.createSubDecor(AppCompatDelegateImpl.java:841)
at androidx.appcompat.app.AppCompatDelegateImpl.ensureSubDecor(AppCompatDelegateImpl.java:806)
at androidx.appcompat.app.AppCompatDelegateImpl.findViewById(AppCompatDelegateImpl.java:630)
at androidx.appcompat.app.AppCompatActivity.findViewById(AppCompatActivity.java:223)
at com.example.projectMP3.SplashScreenActivityTest.testLaunchOfNewActivity(SplashScreenActivityTest.java:14)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:59)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:56)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
at org.junit.runners.BlockJUnit4ClassRunner$1.evaluate(BlockJUnit4ClassRunner.java:100)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:366)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:103)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:63)
at org.junit.runners.ParentRunner$4.run(ParentRunner.java:331)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:79)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:329)
at org.junit.runners.ParentRunner.access$100(ParentRunner.java:66)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:293)
at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
at org.junit.runners.ParentRunner.run(ParentRunner.java:413)
at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)
at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:230)
at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:58)
Program code "SplashScreenActivity.java":
public class SplashScreenActivity extends AppCompatActivity {
LinearLayout linearLayout;
/** Toolbar */
androidx.appcompat.widget.Toolbar toolbar;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_splash_screen);
toolbar = findViewById(R.id.toolBar);
setSupportActionBar(toolbar);
linearLayout = findViewById(R.id.Splash_Activity);
linearLayout.setOnClickListener(v -> {
Intent intent = new Intent(SplashScreenActivity.this, MainActivity.class);
startActivity(intent);
finish();
});
getWindow().setFlags(
WindowManager.LayoutParams.FLAG_LAYOUT_NO_LIMITS,
WindowManager.LayoutParams.FLAG_LAYOUT_NO_LIMITS
);
Objects.requireNonNull(getSupportActionBar()).hide();
Thread thread = new Thread() {
public void run() {
try {
sleep(3000);
} catch (Exception e) {
e.printStackTrace();
} finally {
Intent intent = new Intent(SplashScreenActivity.this,
MainActivity.class);
startActivity(intent);
finish();
}
}
};
thread.start();
}
}
Program code "SplashScreenActivityTest.java":
import android.widget.TextView;
import org.junit.Test;
import static org.junit.Assert.assertNotNull;
public class SplashScreenActivityTest {
#Test
public void testLaunchOfNewActivity() {
SplashScreenActivity activity = new SplashScreenActivity();
TextView nameApplication = activity.findViewById(R.id.textView3);
assertNotNull(nameApplication.getText());
}
}
Program code "activity_splash_screen.xml":
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/Splash_Activity"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#color/colorPrimaryDark"
android:orientation="vertical"
tools:context=".SplashScreenActivity">
<androidx.appcompat.widget.Toolbar
android:id="#+id/toolBar"
android:layout_width="match_parent"
android:layout_height="?actionBarSize"
android:background="#drawable/tab_indicater"
android:theme="#style/ThemeOverlay.AppCompat.Dark.ActionBar" />
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center"
android:orientation="vertical">
<ImageView
android:id="#+id/imageView2"
android:layout_width="320dp"
android:layout_height="320dp"
android:layout_gravity="center_horizontal"
app:srcCompat="#drawable/splash_screen_logo"
android:layout_marginTop="100dp"
app:tint="#120a8f"
android:contentDescription="#string/startSplashScreen" />
</LinearLayout>
<TextView
android:id="#+id/textView3"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:fontFamily="cursive"
android:gravity="center"
android:text="#string/appName"
android:textColor="#FFAB00"
android:textSize="50sp"
android:paddingLeft="30dp"
android:paddingRight="30dp"
android:layout_marginTop="2dp"
android:textStyle="bold" />
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="bottom"
android:orientation="vertical">
<TextView
android:id="#+id/textView"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center"
android:text="#string/all_rights_are_reserved"
android:textColor="#color/white"
android:textSize="15sp" />
</LinearLayout>
</LinearLayout>
This is my first time writing unit tests. I hope for your help! Thank you in advance.

Answer 1

The issue related to your Activity class. You just tried to test activity like a simple class. But in the android, Activity it's a system component managed by the system, and you can't just create an Activity using constructor.
On the official site it has a documentation how to test an activity:
https://developer.android.com/guide/components/activities/testing

Answer 2

It seems you are calling the activity and accessing the UI component in that activity. I don't know if you can do that in unit test without launching the app which makes it Instrumented test(which should be tested with AndroidJunit4)