Testing fixtured for attributes with class name

In rails, a model

belongs_to :production_variety, class_name: 'Categoryminor'

the fixtures for categoryminors.yml has an entry

production_mel_lung:
  id: 113

Yet, when running a test whether any of the following is provided for a fixture in this model's class

one:
  production_variety: production_mel_lung.id

one:
  production_variety: production_mel_lung

one:
  production_variety_id: 113

for the unit test

culture = cultures(:one)
assert culture.valid?, culture.errors.full_messages.inspect

invariably returns

["Production variety must exist"]

Which is incorrect given the model definition. What must be done syntaxically to the fixtures to make this a proper test?