Added an unit test with Plack::Test

Makefile.PL

@@ -2,7 +2,11 @@ use inc::Module::Install;
 name 'HTML-Mason-PSGIHandler';
 all_from 'lib/HTML/Mason/PSGIHandler.pm';
 readme_from 'lib/HTML/Mason/PSGIHandler.pm';
+
+requires 'HTML::Mason';
+
 build_requires 'Test::More';
+test_requires 'Test::Requires';
 use_test_base;
 auto_include_deps;
 author_tests('xt');

t/hello.mhtml

@@ -0,0 +1,4 @@
+% my $var = "Foo";
+Hello World <% $var %>
+<% do { join ",", $r->params } %>
+

t/hello.t

@@ -0,0 +1,23 @@
+use strict;
+use FindBin;
+use Test::More;
+use Test::Requires qw(Plack::Test);
+use Plack::Test;
+
+use HTML::Mason::PSGIHandler;
+
+my $h = HTML::Mason::PSGIHandler->new(
+    comp_root => $FindBin::Bin,
+);
+
+my $handler = sub { $h->handle_psgi(@_) };
+
+test_psgi app => $handler, client => sub {
+    my $cb = shift;
+    my $res = $cb->(HTTP::Request->new(GET => "http://localhost/hello.mhtml?foo=bar"));
+    like $res->content, qr/Hello World Foo/;
+    like $res->content, qr/foo,bar/;
+};
+
+done_testing;
+