GoCardlessClient does not implement an interface, which means it cannot be mocked for testing purposes

[IanKemp]

This is a massive omission that essentially forces consumers to write their own wrappers that do use an interface, which somewhat defeats the purpose of using this package in the first place.

[pencho]

Totally agree! To add to the frustration, the DTOs properties have non-public setters which means that they can not be used in tests.