@Before
public void setup() {
    mActivity = Robolectric.buildActivity(MainActivity.class).create().get();
    mKeyboard = new Scanner(System.in);
}

@Test
public void userInteraction() {
    System.out.println("Enter Username and press Enter : ");
    mUsername = mKeyboard.nextLine();
    System.out.println("Enter Password and press Enter : ");
    mPassword = mKeyboard.nextLine();
    System.out.println("Trying to login...");
}

String data = "Users Input";
System.setIn(new ByteArrayInputStream(data.getBytes()));