Refactor spending_by_practice tests
Refactor spending_by_practice tests

Moving the params from a queystring to a dict gives a bit more clarity
about what's being tested.

ebmdatalab/openprescribing,annapowellsmith/openpresc,annapowellsmith/openpresc,ebmdatalab/openprescribing,ebmdatalab/openprescribing,annapowellsmith/openpresc,ebmdatalab/openprescribing,annapowellsmith/openpresc