java.lang.NullPointerException error in android unit testing

i get java.lang.NullPointerException: Attempt to invoke virtual method error when i try to run my android unit test. code:

public class LoginActivityTest extends ActivityInstrumentationTestCase2<LoginActivity>

{

LoginActivity m_Activity;
LinkableEditText editText;


public LoginActivityTest()
{
    super(LoginActivity.class);
}

@Override
protected void setUp() throws Exception
{
    super.setUp();

    m_Activity = getActivity();

    editText = (LinkableEditText)m_Activity.findViewById(R.id.login_dialog_msisdn);
}

public void testPreConditions()
{
    assertNotNull(editText);
}

@UiThreadTest
public void testEditText()
{
    assertEquals("",editText.getText());
}

im new to unit testing. what should i do in here?