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Promises (control return values) & Arguments

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In our spec, we said that, when we call buildEnclosure(), we expect it to call growVelociraptor() on DinosaurFactory and pass it the exact argument 5. There was no super cool or secret reason for that: it's just how we decided to make this method work: all dinosaurs would have this same length. And when it calls growVelociraptor() with an argument of 5, we said that it should return $dino1 the first time it's called and $dino2 the second time.

Calling a Stubbed Method with a Different Argument

But... what if it weren't that simple? Go into the service. Making every dinosaur the same size isn't very realistic. No, let's make it more interesting - let's make the length 5 + $i. So 5, then 6, 7 and so on.

50 lines | src/Service/EnclosureBuilderService.php
// ... lines 1 - 40
private function addDinosaurs(int $numberOfDinosaurs, Enclosure $enclosure)
for ($i = 0; $i < $numberOfDinosaurs; $i++) {
$this->dinosaurFactory->growVelociraptor(5 + $i)
// ... lines 49 - 50

What will phpspec think of this? Our example still says that we expect this method to always be called with the argument 5. Well... let's find out!

./vendor/bin/phpspec run spec/Service/EnclosureBuilderServiceSpec.php:19

It fails! And check this out! It says:

Unexpected method call on DinosaurFactory, growVelociraptor(6). Expected was growVelociraptor(5)

The way this fails is the really important part. When you call willReturn(), this is called a method promise. You're making a promise that the growVelociraptor() method will return this $dino1 value and then this $dino2 value. As soon as you apply even one promise to one method on a dummy object, you must apply a promise to every single call.

This can be a little tricky to understand at first. When we say $dinosaurFactory->growVelociprator(5)->willReturn(), we're really saying:

Hey phpspec! When growVelociraptor() is called and passed 5 as an argument, you should return $dino1 and $dino2. If any other value is passed, this promise doesn't apply.

So, when growVelociraptor() is called with 6 as an argument, it looks at this promise and determines it doesn't apply. But, once you define even one promise, you must define a promise... basically, you must tell phpspec what to do for every method call and every possible argument.

In other words, the simplest way to fix this would be to add a promise for every argument that we'll pass - like $dinosaurFactory->growVelociraptor(6)->willReturn(), then 7, 8, 9 - however many you need for that example. Whenever growVelociraptor() is called, prophecy goes down all of the promises for that method and finds the one that fits best. If none are found... but at least one is specified... error!


Of course... creating a promise for every possible argument is... a bit nuts. So what's the real fix? Remove the specific argument 5 and replace it with a special Argument class from prophecy and pass it any(). Try phpspec again:

// ... lines 1 - 18
function it_builds_enclosure_with_dinosaurs(DinosaurFactory $dinosaurFactory)
// ... lines 21 - 25
// ... lines 27 - 28
// ... lines 30 - 36
// ... lines 38 - 39
./vendor/bin/phpspec run spec/Service/EnclosureBuilderServiceSpec.php:19

We're back! This says:

Yo phpspec! It's me again, Ryan. So, when growVelociraptor() is called with any argument, here's what you should return.

Thanks to this, every time we call growVelociraptor() - regardless of the arguments passed to it - this promise will be matched.

Other ways to Specify Arguments

Oh, and if we were passing growVelociraptor() two arguments, then we would need to also pass two arguments here. If you don't care, just use Argument::any(). Or, if you had a third argument and wanted this promise to be used no matter what values were passed, you can use cetera().

But sometimes, I want to be a bit more specific. For example, we don't really want growVelociraptor() to be called with any argument: it should be an integer at least! If you really want to make sure that's happening correctly, you can use Argument::type() and pass integer.

// ... lines 1 - 25
// ... lines 27 - 39

This should work for us... so let's try it!

./vendor/bin/phpspec run spec/Service/EnclosureBuilderServiceSpec.php:19

All green! But now change this to string. Try it again:

// ... lines 1 - 25
// ... lines 27 - 39
./vendor/bin/phpspec run spec/Service/EnclosureBuilderServiceSpec.php:19

Yes! Unexpected method call on growVelociraptor(5). When the integer 5 is passed, phpspec says:

Hey, somebody is calling growVelociraptor() with an argument that doesn't match any of the promises for this method. That's probably not expected, so I'm gonna go ahead and explode. Cheers!

The most flexible Argument is called that(). I won't show an example, but Argument::that() allows you to pass a callback function. It passes your callback the argument and then you can do whatever logic you need to determine if this is something you're expecting or not.

Let's change this back to type('integer'). And here is where things get truly interesting. We know that growVelociraptor() is going to be called two times. And so, to take super crazy control of things, we can create two separate method promises to handle each one. If you don't fully understand how this Argument stuff works yet, you will next.