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<a href="/" class="homelink">Dancer Advent Calendar</a><br />

<p>
The PerlDancer Advent Calendar is a community-driven project that aims 
to showcase the Dancer Perl web framework.
</p>

<p>
Each day of December until Christmas, one article about Dancer. Stay tuned for new moves!
</p>

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    <h3>About Dancer</h3>
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        <li><a href="http://www.perldancer.org/">Dancer homepage</a></li>
        <li><a href="http://twitter.com/PerlDancer">Official Twitter</a></li>
        <li><a href="http://github.com/PerlDancer/Dancer">Dancer on GitHub</a></li>
        <li><a href="http://github.com/PerlDancer/Dancer2">Dancer 2 on GitHub</a></li>
        <li><a class="feed" href="/feed/2018">RSS</a></li>
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<div class="pod-document"><h1><a name="testing_dancer_with_test__mojo"></a>Testing Dancer with Test::Mojo</h1>

<p>Authors of Dancer (and other) PSGI applications are probably accustomed to <a href="https://metacpan.org/pod/distribution/Dancer2/lib/Dancer2/Manual.pod#TESTING">testing</a> with <a href="https://metacpan.org/pod/Plack::Test">Plack::Test</a>, and ...
<p>During advent last year, I wrote about <a href="https://mojolicious.org/perldoc/Test/Mojo">Test::Mojo</a>, showing the many easy and (dare I say) fun ways that you can use it to test your Mojolicious applications.
If you missed it, go <a href="https://mojolicious.io/blog/2017/12/09/day-9-the-best-way-to-test/">check it out</a>.</p>
<p>I expect there are at least a few of you out there who read that and think, "I'd love to use that, but I don't use Mojolicious!"; well, you're in luck!
With just a little role to bridge the gap, you can use Test::Mojo to test your PSGI applications too!</p>
<h2><a name="mounting_psgi_applications"></a>Mounting PSGI Applications</h2>

<p>Mojolicious itself doesn't use the <a href="https://metacpan.org/pod/PSGI">PSGI</a> protocol, owing to certain features that it doesn't provide and which are necessary for certain asynchronous operations.
That said, you can serve a Mojolicious application on a PSGI server by using <a href="https://mojolicious.org/perldoc/Mojo/Server/PSGI">Mojo::Server::PSGI</a>.
This Mojolicious-core module is automatically used for you when your Mojolicious-based app detects that it has started under a PSGI server (e.g. plackup or Starman).</p>
<p>While translating between a Mojo app and a PSGI server is core functionality, doing the opposite, translating between a PSGI app and a Mojolicious server (or app, as you'll see) is available as a third party module.
<a href="https://metacpan.org/pod/Mojolicious::Plugin::MountPSGI">Mojolicious::Plugin::MountPSGI</a>, as it's name implies, can mount a PSGI application into a Mojolicious-based one.
To do so, it builds a new, empty Mojolicious application that translates all requests to PSGI environments before dispatching to it as with any <a href="https://mojolicious.org/perldoc/Mojolicious/Plugin/Mount">mount</a>-ed application.</p>
<h2><a name="testing_using_test__mojo"></a>Testing using Test::Mojo</h2>

<p>Once you can do that, it is trivial to take a PSGI application, wrap it with MountPSGI, and set it as the application for use with Test::Mojo.
Still, to make it even easier, that has all been done for you in <a href="https://metacpan.org/pod/Test::Mojo::Role::PSGI">Test::Mojo::Role::PSGI</a>.</p>
<p>Like any <a href="https://mojolicious.io/blog/2017/12/13/day-13-more-about-roles/">Mojolicious Role</a>, we can use <code>with_roles</code> to create a (mostly anonymous) subclass with the role applied.
You can use the shortcut <code>+</code> to stand in for <code>Test::Mojo::Role::</code>.</p>
<pre class="prettyprint">use Test::Mojo;
my $class = Test::Mojo-&gt;with_roles('+PSGI');</pre>

<p>Then you instantiate that role with the path to the PSGI application, or else the PSGI application itself.</p>
<p>Since you're using roles, which are all about composition, you can also apply other roles that you might <a href="https://metacpan.org/search?q=%22Test%3A%3AMojo%3A%3ARole%22">find on CPAN</a>.</p>
<h2><a name="an_example"></a>An Example</h2>

<p>As an example, let's say we have a simple application script (named <code>app.psgi</code>) that can render a <code>"hello world"</code> or <code>"hello $user"</code> in several formats.
I'll allow a plain text response, JSON, and templated HTML (using the <a href="https://metacpan.org/pod/Dancer2::Template::Simple">simple</a> template to keep this concise).</p>
<pre class="prettyprint">use Dancer2;

set template =&gt; 'simple';
set views =&gt; '.';

any '/text' =&gt; sub {
  my $name = param('name') // 'world';
  send_as plain =&gt; "hello $name";

devdata/http_advent.perldancer.org_2018_20  view on Meta::CPAN 

That would be a monstrous regexp (hehe).
However it is a piece of cake using <a href="https://mojolicious.org/perldoc/Mojo/DOM/CSS">CSS Selectors</a>.</p>
<pre class="prettyprint">$t-&gt;get_ok('/html')
  -&gt;status_is(200)
  -&gt;content_type_like(qr[text/html])
  -&gt;text_is('dl#data dt#hello + dd', 'world');

$t-&gt;post_ok('/html' =&gt; form =&gt; { name =&gt; 'grinch' })
  -&gt;status_is(200)
  -&gt;content_type_like(qr[text/html])
  -&gt;text_is('dl#data dt#hello + dd', 'grinch');

done_testing;</pre>

<p>In this year's Mojolicious advent calendar, we've already seen <a href="https://mojolicious.io/blog/2018/12/05/compound-selectors/">some</a> <a href="https://mojolicious.io/blog/2018/12/14/a-practical-example-of-mojo-dom/">great</a> <a href="https...
The point remains however, testing HTML responses with CSS selectors allows you to make your tests targetd in a way that allows you to write more and better tests since you don't have to hack around extracting the bits you want.</p>
<h2><a name="testing_websockets"></a>Testing WebSockets</h2>

<p>Ok so that's great and all, but of course now it comes to the point you've all been waiting for: can you test WebSockets?
As Jason Crome mentioned in his <a href="http://advent.perldancer.org/2018/13">Twelve Days of Dancer</a> "State of Dancer", you can now dance with WebSockets via <a href="https://metacpan.org/pod/Dancer2::Plugin::WebSocket">Dancer2::Plugin::WebSocket...
<p>Well, so far not via the role I showed above.
It might be possible, but it would involve learning deep PSGI magick that I'm not sure I'm smart enough to do; patches welcome obviously :D.</p>
<p>Still I mentioned above that Test::Mojo can test anything it can access via an fully qualified URL, so let's just start up a server and test it!
I'll use the <a href="https://github.com/yanick/Dancer2-Plugin-WebSocket/tree/releases/example">example bundled with the plugin</a> for simplicty.</p>
<pre class="prettyprint">use Mojo::Base -strict;

use EV;
use Test::More;
use Test::Mojo;

use Twiggy::Server;
use Plack::Util;

my $app = Plack::Util::load_psgi('bin/app.psgi');
my $url;
my $twiggy = Twiggy::Server-&gt;new(
  host =&gt; '127.0.0.1',
  server_ready =&gt; sub {
    my $args = shift;
    $url = "ws://$args-&gt;{host}:$args-&gt;{port}/ws";
  },
);
$twiggy-&gt;register_service($app);</pre>

<p>This starts Twiggy bound to localhost on a random port and starts the application using it.
When the server starts, the actual host and port are passed to the <code>server_ready</code> callback which we use to build the test url.
Now you just create a Test::Mojo instance as normal but this time open a websocket to the fully-qualified url that we built above.</p>
<pre class="prettyprint">my $t = Test::Mojo-&gt;new;

$t-&gt;websocket_ok($url)
  -&gt;send_ok({json =&gt; {hello =&gt; 'Dancer'}})
  -&gt;message_ok
  -&gt;json_message_is({hello =&gt; 'browser!'})
  -&gt;finish_ok;

done_testing;</pre>

<p>Unlike the previous examples, this time the connection stays open (but blocked) between method calls.
Per the protocol of the example, we first send a greeting to the Dancer app as a JSON document.
Since so much real-world websocket usage is just serialized JSON messages, Mojolicious provides many JSON-over-WebSocket conveniences.
One such convenience is a virtual websocket frame type that takes a data structure and serializes it as JSON before actually sending it as a text frame.</p>
<p>We then wait to get a message in response with <code>message_ok</code>.
In this case, we expect the application to greet us by calling us "browser!".
Oh well, it doesn't know any better!
We can the test that JSON reply with <code>json_message_is</code> (like <code>json_is</code> above but for websocket messages).
Finally we close the connection, testing that it closes correctly.</p>
<p>Testing WebSockets, even from a Dancer application, is easy!</p>
<h2><a name="conclusion"></a>Conclusion</h2>

<p>Although there are some great testing options in the PSGI space, Test::Mojo has lots of benefits for Dancer and PSGI users.
By using Test::Mojo::Role::PSGI or by running against a locally-bound server, Test::Mojo can be a tool in the toolbox of any PSGI developer.</p>
<h2><a name="author"></a>AUTHOR</h2>

<p>Joel Berger (<a href="https://twitter.com/joelaberger">@joelaberger</a>) has Ph.D. in Physics from the University of Illinois at Chicago. 
He is an avid Perl user, <a href="https://metacpan.org/author/JBERGER">author</a>, and is a member of the Mojolicious Core Team.</p>
<h2><a name="copyright"></a>COPYRIGHT</h2>

<p>Copyright (c) 2018 Joel Berger</p>
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