JMS\Serializer\Annotation\Type does not exist or not found

I am working on writing tests for some existing code. The code works, but if I write a unit test that hits the same code, I get this error:

Doctrine\Common\Annotations\AnnotationException : [Semantical Error] The annotation "@JMS\Serializer\Annotation\Type" in property App\DTO\ItemDataCostValue::$available does not exist, or could not be auto-loaded.

The annotation for that property exists and I can click through to it:

use JMS\Serializer\Annotation\ as JMS;

class ItemDataCostValue
{
    /**
     * @var boolean
     * @JMS\Type("boolean")
     * @JMS\SerializedName("f")
     * @JMS\SkipWhenEmpty
     */
    protected $available;

It seems like this line is causing the error:

$idc = $this->serializer->deserialize($amenity->getData(), ItemDataCostValue::class, 'json');

The serializer is built in my test like this:

$accommodationAmenities = new AccommodationAmenitiesBusinessCase(
    new AccommodationDataService($accommodationRepositoryMock),
    new FieldsService($fieldRepositoryMock),
    new ValueTypeService($valueRepositoryMock),
    SerializerBuilder::create()->build(),
    new CostObjectsHelpers()
);

The constructor looks like this:

public function __construct(
    AccommodationDataService $dataService,
    FieldsService $fieldsService,
    ValueTypeService $valueTypeService,
    SerializerInterface $serializer,
    CostObjectsHelpers $costHelpers
) {
    $this->dataService = $dataService;
    $this->fieldsService = $fieldsService;
    $this->valueTypeService = $valueTypeService;
    $this->serializer = $serializer;
    $this->costHelpers = $costHelpers;
}

Am I building the serializer wrong? Is there something I should check in my config? What could be the problem?