How to test if Snackbar is shown in android

on Any click event i have to test a Snackbar is shown i created a custom shadow Snackbar using :https://github.com/cafesilencio/snackbarshadow

and in testing i called it as::

    registerBtn.performClick();
    Snackbar snack = ShadowSnackbar.getLatestSnackbar(); // i always get null here
    assertNotNull(snack); //fails
    ShadowSnackbar shadowSnackbar = ShadowSnackbar.shadowOf(ShadowSnackbar.getLatestSnackbar());
    assertEquals("asdasd",shadowSnackbar.getTextOfLatestSnackbar());

any help guyss!!!