@Test
public void shouldInjectDefaultSharedPrefs() throws Exception {

    final A a = Robolectric.buildActivity(A.class).create().get();
    final Field f = TestSharedPreferences.class.getDeclaredField("filename");
    f.setAccessible(true);
    assertTrue(Strings.notEmpty(f.get(a.prefs)));
    assertThat(f.get(a.prefs), equalTo(f.get(PreferenceManager.getDefaultSharedPreferences(a))));
}