Introducing Magpie – flexible test doubles & mocking for Perl

November 19, 2010 § 3 Comments


Magpie is a new distribution I have just released which brings the power of test doubles to Perl. There are already a few solutions to test doubles in Perl, but Magpie takes a different approach. Inspired heavily by Mockito for Java, Magpie gives you test doubles that are based are spying and verification, not expectations. So, before we really dive into it, how does it look?

use Test::Magpie qw( mock when );
use Test::More;
my $mocked_list = mock;


is($mocked_list->get(0) => 'first');
ok(exception { $mocked_list->get(1) });
is($mocked_list->get => undef);

So, what’s going on here? First of all we create a mock object. This object does every role, is a subclass of every class, and can run any method (returning undef by default). We then stub this object to handle some method calls using the when construct. We specify that when we request item 0 from our mocked list we should return the string ‘first’ and when request item 1, we throw an exception string ‘Kaboom!’. Simple! And as you can see, the tests following all verify this behaviour – this example is straight out of t/mockito_examples.t

What does Magpie have to offer?

What you just saw was the basics of Magpie – there are a lot more cool features available, that come in to be very useful!


As well as stubbing methods, you can also verify that methods were called. The following example from the synopsis illustrates how this may be useful:

use Test::Magpie qw( mock verify when );

my $baker = mock;
my $bakery = Bakery->new( bakers => [ $baker ] );
my $bread = $bakery->buy_loaf( amount => 2, type => 'white' );
verify($baker, times => 2)->bake_loaf('white');

As you can see, we are able to verify a method was called, and also add some extra details – for now the amount of times a method was called, and which arguments it was called with.

Argument matchers

Argument matchers allow you to be more general in your specification for stubs and verification. Rather than saying “when this method is called with exactly these arguments” we can say the more general “when this method is called with arguments that match these predicates.” In practice, it might look like this:

when($child)->eat(type(SugaryGoodness))->then_return('Ooo, yum!')

In this example Broccoli and SugaryGoodness are type constraints. There are already a few argument matchers that ship with Magpie, and it’s trivial to define your own with the custom_matcher generator.

Extra extra! Read more about it!

There’s more to Test::Magpie than what I’ve mentioned in this post, but if you’re interested, I recommend the official documentation. The basic and Mockito example tests serve as a great demonstration of how Magpie can be practically used.

Go go gadget CPAN – installing Magpie

Magpie is already available for use now, and is on cpan:

cpan Test::Magpie

From your shell, or however you wish to install CPAN modules

I really hope you enjoy this module, I’m already finding it powerful enough to use at work. If you have any criticisms, bugs, feature requests, or ponys to give me – drop me a comment here, an issue on RT, or poke me on IRC (I’m ocharles).

Happy testing!

Edit: 0.04 had a release problem and might not have installed cleanly. 0.05 should fix this. Sorry!

Rocket powered rollerskates templating with HTML::Zoom & Catalyst

March 20, 2010 § 1 Comment

Matt Trout has produced yet more Perl magic with a new templating system – HTML::Zoom. I’d accuse him of committing a cardinal sin, but I guess we can let him off seeing as it’s badass.

A templating engine isn’t much use unless we’ve got something to drive it – and what’s a more natural choice than Catalyst? As always, Catalyst makes gluing things together trivial – so I’ve adopted some prior art from t0m and released Catalyst::View::HTML::Zoom. Now, this is version 0.001 so it wouldn’t be complete without a big fat blinking disclaimer: we might have done this wrong. I chatted about it briefly in #catalyst before starting work, but I still could have got it wrong! So the API could change and everything might blow up in your face… but that’s the fun, right?

Anyway, here’s a brief look at how we’ve got it structured at the moment (shamelessly plagiarized from my own CPAN synopsis):

package MyApp::View::HTML;
use Moose;
extends 'Catalyst::View::HTML::Zoom';

package MyApp::Controller::Wobble;
use Moose; BEGIN { extends 'Catalyst::Controller' }
sub dance : Local {
    my ($self, $c) = @_;
    $c->stash( shaking => 'hips' );

package MyApp::View::HTML::Controller;
use Moose;
sub dance {
    my ($self, $stash) = @_;

<p>Shake those <span id="shake" />!</p>

/wobble/dance => "<p>Shake those <span id="shake">hips!</span></p>";

The key class here is MyApp::View::HTML::Wobble which does the HTML::Zoom substitutions. $_ is locally aliased to the HTML::Zoom object for convenience and the first parameter is the stash object.

Happy hacking – let’s see where this ends up!

Marketing & CPAN – follow up and an example of changes

March 16, 2010 § 7 Comments

If you read my last post, you will have heard me complaining about’s interface about providing documentation. I argued that the quality of documentation was mixed, though the big projects (where it’s important to get as much wow factor as possible) had some great writing. However, the presentation is thoroughly lacking.

I don’t like complaining without trying to actually help, so I spent a bit of my free time today by making something that tries to incorporate the changes I mentioned.

A Catalyst documentation landing page

It’s probably lacking a little in the punch visually, but just look at that structure. As a new user I’ve got plenty of documentation about getting started – as a developer I’ve got easy access to the important APIs, and if I’m getting really geeky, there’s material for me to geek out with.

Now I should emphasize. None of this content is new – every single one of this pages mirrors something in the Catalyst::Manual. But I think that added structuring and a few explanatory paragraphs has made a world of difference. This change carries over nicely to the documentation pages themselves:

Viewing some Catalyst documentation

A readable structure, and I can jump straight into the content. If you think these arguments still hold for Catalyst, clearly you seen some of the pages…

I should stress that this is nothing more than an idea in my head at the moment. The above aren’t lockups, they are brain dumps. But I’m really keen to try and make this reality – I just don’t know enough about the Perl community to know who to talk to in order to get it done. So, if you want to talk about this – leave some comments and we’ll work something out 🙂 Even advice on who to talk too is much appreciated!

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