PHPSpec

Dependency.php

<?php

namespace Acme;

use Acme\SubDependency;

class Dependency
{
    protected $subDep;

    function __construct(SubDependency $subDep)
    {
        $this->subDep = $subDep;
    }

    function getRender()
    {
        return $this->subDep->render();
    }
}

RoadRunner.php

<?php

namespace Acme;

use Acme\Dependency;

class RoadRunner
{
    protected $dep;
    
    public function __construct(Dependency $dep)
    {
        $this->dep = $dep;
    }

    public function letsGo()
    {
        return $this->dep->getRender();
    }
}

RoadRunnerSpec.php

<?php

namespace spec\Acme;

use PhpSpec\ObjectBehavior;
use Prophecy\Argument;
use Acme\Dependency;
use Acme\SubDependency;

class RoadRunnerSpec extends ObjectBehavior
{
    
    function let(Dependency $dependency)
    {
        
        // This injects Dependency (subject) into the RoadRunner object but leaves out SubDep from Dependency?
        $this->beConstructedWith($dependency)
    }
    
    function it_is_initializable()
    {
        $this->shouldHaveType('Acme\RoadRunner');
    }

    function it_should_return_dep()
    {
        // This should return hello world if all dependencies are set up correctly
        $this->letsGo()->shouldReturn('Hello World');
    }
}

SubDependency.php

<?php

namespace Acme;

class SubDependency
{

    public function render()
    {
        return 'Hello world';
    }

}

Now question is how to get the phpspec to pass by injecting the dependencies

Sounds like you want something along the lines of this? I don't know much more than that though:

<?php

namespace spec\Acme;

...
use Acme\DerpDep;

class RoadRunnerSpec extends ObjectBehavior
{
    ...
    function let($derp)
    {
        $this->beConstructedWith($derp);
    }
}

http://www.phpspec.net/docs/introduction.html#let-and-let-go

That's cool yea I got that far... my issue is getting DerpDep injected into TestDep before injecting that into roadrunner

I did think it could be done by writing...

<?php
...

function let(Dependency $dependency, SubDependency $subdep)
{
    $dependency->beConstructedWith([$subdep]);
    $this->beConstructedWith($dependency)
}

But this throws a typecasting error because the object is actually of the type PhpSpec\Wrapper\Collaborator.

So we can get the wrapped object by calling getWrappedObject() like so

<?php
...

function let(Dependency $dependency, SubDependency $subdep)
{
    $dependency->beConstructedWith([$subdep->getWrappedObject()]);
    $this->beConstructedWith($dependency)
}

This will fix the error but does not make the test pass so we're back to square 1 again

I don't have much more advice I'm afraid, my experience with PHPSpec was limited to trying to get it working in a DI scenario, which I quickly established couldn't be done easily since it's designed to construct objects itself, so I switched back to PHPUnit, good luck with it if you haven't solved the problem already!

<?php

namespace spec\Acme;

use PhpSpec\ObjectBehavior;
use Prophecy\Argument;
use Acme\Dependency;
use Acme\SubDependency;

class RoadRunnerSpec extends ObjectBehavior
{
    function let(Dependency $dependency)
    {
        // You don't care about SubDependency here! You only interact with direct collaborator.
        $this->beConstructedWith($dependency)
    }

    function it_is_initializable()
    {
        $this->shouldHaveType('Acme\RoadRunner');
    }

    function it_renders_a_string(Dependency $dependency)
    {
        $dependency->getRender()->willReturn('Hello World');

        // letGo() returns whatever the Dependency returned, 
        // you should spec Dependency::getRender() in the DependencySpec
        $this->letsGo()->shouldReturn('Hello World');
    }
}