XML : Unit testing in Android Studio returns NullPointerException

I am having trouble implementing a JUnit test in my android studio project. What I have done is make a class extending AppCompatActivity called SellerMainPage. On this page, I have a TextView. I would like to check that the page opens up correctly and that the TextView is set to the right value. But I get a NullPointerException thrown in the SetUp() function coming from setting the TextView to the seller_main_page.xml file that corresponds to the SellerMainPage.java file.

The line

  tv = (TextView) page.findViewById(R.id.textView9);    

is where I think the problem is coming from. I have checked that this is indeed the TextView from the .xml document, so I do not know why I get the error.

SellerMainPageTest.java

  package com.example.cristiannavarrete.my_shopping;    import android.test.ActivityInstrumentationTestCase2;  import android.widget.TextView;    import junit.framework.TestCase;    import org.w3c.dom.Text;    import java.util.ArrayList;    /**   * Created by Cristian Navarrete on 12/1/2015.   */  public class SellerMainPageTest extends ActivityInstrumentationTestCase2<SellerMainPage> {        private SellerMainPage page;      private TextView tv;        @SuppressWarnings("deprecation")      public SellerMainPageTest() {          super("com.example.cristiannavarrete.my_shopping.SellerMainPage", SellerMainPage.class);      }        @Override      protected void setUp() throws Exception {          super.setUp();          page = this.getActivity();            tv = (TextView) page.findViewById(R.id.textView9);        }        public void testPreconditions() {          assertNotNull("page is null", page);          assertNotNull("tv is null", tv);      }    }    

Here is the corresponding xml file

seller_main_page.xml

  <?xml version="1.0" encoding="utf-8"?>  <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"  android:layout_width="match_parent" android:layout_height="match_parent"  android:id="@+id/sellerName">    <RelativeLayout      android:orientation="horizontal"      android:layout_width="match_parent"      android:layout_height="match_parent">        <Button          android:layout_width="wrap_content"          android:layout_height="wrap_content"          android:layout_gravity="left"          android:text="@string/addProduct"          android:id="@+id/addProduct"          android:layout_alignParentTop="true"          android:layout_alignParentLeft="true"          android:layout_alignParentStart="true" />        <Button          android:layout_width="wrap_content"          android:layout_height="wrap_content"          android:layout_gravity="right"          android:text="@string/viewFinances"          android:id="@+id/seeFinances"          android:layout_alignParentTop="true"          android:layout_alignParentLeft="true"          android:layout_alignParentEnd="true" />        <LinearLayout          android:orientation="vertical"          android:layout_width="match_parent"          android:layout_height="match_parent"          android:layout_below="@+id/addProduct"          android:layout_centerHorizontal="true">            <TextView              android:layout_width="wrap_content"              android:layout_height="wrap_content"              android:textAppearance="?android:attr/textAppearanceLarge"              android:text="@string/sellerInventory"              android:id="@+id/textView9"              android:layout_gravity="center_horizontal"              android:textStyle="bold"              android:textColor="#4aa260"              android:textSize="25dp" />            <ScrollView              android:layout_width="match_parent"              android:layout_height="365dp"              android:id="@+id/scrollView"              android:layout_gravity="center_horizontal" >                <LinearLayout                  android:orientation="vertical"                  android:layout_width="match_parent"                  android:layout_height="wrap_content"                  android:id="@+id/sellerListScroll"></LinearLayout>          </ScrollView>            <Button              android:layout_width="wrap_content"              android:layout_height="wrap_content"              android:text="@string/goBack"              android:id="@+id/sellerGoBackButton" />      </LinearLayout>  </RelativeLayout>    

Here is my Log:

  java.lang.NullPointerException  at com.example.cristiannavarrete.my_shopping.SellerMainPageTest.setUp(SellerMainPageTest.java:30)  at org.junit.internal.runners.JUnit38ClassRunner.run(JUnit38ClassRunner.java:86)  at org.junit.runner.JUnitCore.run(JUnitCore.java:137)  at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:78)  at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:212)  at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:68)  at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)  at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)  at com.intellij.rt.execution.application.AppMain.main(AppMain.java:140)    

Can someone help explain this to me?