// Test that certain functionality was called
@Test
public void buttonShouldDoSomethingCrazy() throws Exception {
    button.performClick();
    assertTrue(activity.conditionWasMet);
}

// Mock class
class TestNewActivity extends NewActivity {
    protected boolean conditionWasMet = false;

     @Override
     protected void doSomethingCrazy() {
        conditionWasMet = true;
    }
}

// Original class
public class NewActivity extends Activity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.new_activity);

        View button = findViewById(R.id.crazy_button);
        button.setOnClickListener(new View.OnClickListener() {
            public void onClick(View view) {
                doSomethingCrazy();
            }
        });
    }

    protected void doSomethingCrazy() {}
}