Create an IndexingService responsible for indexing resources

The description is for ".update_index". So this is not actually testing what .update_index is supposed to do. Furthermore there is a nearly identical test here (for .to_solr): https://github.com/projecthydra/active_fedora/blob/solr_indexer_service/spec/unit/base_spec.rb#L319 So, I'm calling this test a duplicate.