JMS Serializer not reading config when running PHPUnit tests in Symfony2

I'm using JMSSerializer to create JSON responses for a Symfony2 project I'm working on and a trying to build unit tests for each response but I'm hitting variations of the below: ``` JMS\Serializer\Exception\RuntimeException: You must define a type for FooBundle\Entity\Bar::$name. ``` I'm using YML config for the serializer and it works perfectly when generating responses. ``` #src/FooBundle/Resources/config/serializer/Entity.Bar.yml FooBundle\Entity\Bar: exclusion_policy: none properties: id: exclude: true type: integer name: type: string ``` I wondered if I need to preload the config somehow and found this link: http://jmsyst.com/libs/serializer/master/configuration that says to configure a metadata path but also to include a file suffix: ``` $serializer = JMS\Serializer\SerializerBuilder::create() ->addMetadataDir($someDir) ->build(); ``` I've tried setting the config directory when generating the serializer in the unit test: ``` $serializer = SerializerBuilder::create()->addMetadataDir('path-to-dir')->build(); ``` But this didn't resolve the problem, I checked the documentation page again and it tells you to list a full path to a file "So, if you class would be named Vendor\Package\Foo, the metadata file would need to be located at $someDir/Vendor.Package.Foo.(xml|yml)." but trying get generates: ``` JMS\Serializer\Exception\InvalidArgumentException: The directory "path-to-file" does not exist. ``` Am I missing something obvious? Thanks Ben