How to run unit tests on methods in an Android activity?

Working on an Android app in Android Studio. I am trying to write unit tests for methods in my activity LoginPage. However, I am clearly missing something big. I figure that I would need to make an instance of LoginPage and call the methods from that instance to test them. However, when I try to do this, I get a NullPointerException for anytime I tried to access that object. How do I test these Activity-specific methods if I can't have an instance of the Activity? I figured one solution would be to make every data field in the Activity static, but I feel like that would be considered sloppy coding.

import android.app.Activity;
import android.content.Context;

import org.junit.After;
import org.junit.Before;
import org.junit.Rule;
import org.junit.Test;
import org.junit.runner.RunWith;
import static org.junit.Assert.*;

public class LoginPageTest {

    LoginPage myObjectUnderTest;


    public static final String FAKE_USERNAME = "rodneyram";


    @Before
    public void onLaunch() { myObjectUnderTest = new LoginPage();
    }


    @Test
    public void username_EditText_Test() {

        //Test if the usernameID editText widget correctly gets the written username.

        myObjectUnderTest.usernameID.setText("");
        myObjectUnderTest.usernameID.append(FAKE_USERNAME);
        String testString = myObjectUnderTest.usernameID.getText().toString();
        assertEquals(testString, FAKE_USERNAME);
    }

     @After
        public void tearDown() {
            myObjectUnderTest = null;
     }

}

My error message:

java.lang.NullPointerException
    at com.example.donapp.LoginPageTest.password_EditText_Test(LoginPageTest.java:51)
    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:50)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
    at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
    at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
    at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
    at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
    at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70) ``