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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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