Add testing for query caching

[xtrojak]

To avoid multiple execution of the same API queries, the Converter class has cache implemented. This needs to be properly tested.

[xtrojak]

Make sure lru_cache works correctly with self attribute, as pointed in this PR.

[martenson]

Even if the session is hashable and a singleton I am not sure it makes sense to include it in the cache fingerprint. The response body should be independent of session unless the API does weird things I think?

[martenson]

Should this really be closed?

[xtrojak]

I guess you are right. Any suggestions how to solve this? I would like to keep query_the_service as a method of the class Converter.

[martenson]

We could run the test with actual API calls, CI can handle that. Or are you asking re: my session comment above?

[xtrojak]

Test could be improved using stored info in cach_info.