Assume you have a AnsibleDistribution whose repository_version is a RespotoryVersion with content in it. This would be created like this: https://github.com/pulp/pulp_ansible#create-a-distribution-for-a-repositoryversion
1. Request a content unit from the repo and assert the contents are correct.
2. Create a new RepositoryVersion that removes the unit and do *not* modify the AnsibleDistribution
3. refetch the same content unit and verify it 404s