public function test_apply_filters_with_callback() {
    $a             = new MockAction();
    $callback      = array( $a, 'filter' );
    $hook          = new WP_Hook();
    $tag           = __FUNCTION__;
    $priority      = rand( 1, 100 );
    $accepted_args = rand( 1, 100 );
    $arg           = __FUNCTION__ . '_arg';

    $hook->add_filter( $tag, $callback, $priority, $accepted_args );

    $returned = $hook->apply_filters( $arg, array( $arg ) );

    $this->assertSame( $returned, $arg );
    $this->assertSame( 1, $a->get_call_count() );
  }