....
  $self->tmpl_path(
        [   $ENV{MV_CUSTOM_HTML_TEMPLATE_DIR},
            $ENV{MV_DEFAULT_HTML_TEMPLATE_DIR}
        ]
    );
...

##</code><code>##

   my $tmpl = $self->load_tmpl('login.tmpl')
        or die "Failed to open template file 'login.tmpl'";

##</code><code>##

use Test::Exception;
...
sub show_login_page : Tests(1) {
    my $app = shift->{rm_show_login_page};
    $app->tmpl_path( [] );
    dies_ok { $app->run() } 'dies if missing template file';
}