Implement Nordigen/GoCardless test mode #139
Description
The rate limits are making it very difficult to actually test changes affecting how GoCardless transactions are sent to ynab. For any change, you'll have to wait several hours. Thus, if there are many iterations, it may actually take days to make any meaningful change to GoCardless module.
Aside from requisition creation/renewal, it'd be actually fairly straightforward to 'simulate' the connection by reading data prepated beforahand from json files on disk and present these to the other layears as supposedly coming from GoCardless. Of course, this data would stay pretty much the same but could also be expanded to cover new banks/cases whatever.
Generator(somewhat poorly documented) does not completely cut it as it does not go through all the translation layers now in Nordigen. Furthermore, it generates semirandom data whereas with Nordigen test mode you could have pregenerated data with static expected result flowing in to the YNAB side.
Of course, this would also require the writer to be set to json in most cases.