use Test::More qw(no_plan);
use Test::HTML::Lint;
use WWW::Mechanize;

my $a = WWW::Mechanize->new();
$a->get( $url );
is( $a->status, 200, 'Fetched OK' );
like( $a->content,  qr/Details/,  "Correct page");
html_ok( $a->content, "Details HTML" );

$a->form_name('details');
$a->field( a_radio_button => 'invalid_value' ); # <-- dies here
$a->click();