@nz, not quite following you. I realize now I did not add any examples in the api spec, so I'm doing that now. And I'll make sure each line of code is properly exercised. But, having trouble thinking of a specific scenario that would cause this line to fail unexpectedly. I'm sure there are many, but not being the expert, they don't come to mind. I could make mocks that have a wacky solr_response_header['params']['fq'] and guard against that? If you have a specific idea in mind, please do let me know.