Write more intensive automated tests

[zoedsoupe]

Chore

Describe the chore

I think it's valuable to write automated tests. Since we're using an external service (postgrest) it need to be mocked, so we also don't want to write "totally mocked tests" since it will be very biased, so i suggest to use something like ex_cvr to make real requests to the dev server and records responses, so we can indeed test all expression with real data at least "once".

Additional context

N/A

[zoedsoupe]

when i developed the library i manually tested some expression but some others not and i want to avoid things like #2 for example