How to write practical tests to an app (or piece of code )that all it does take data from a REST service process it and send it to another service ?

Hi I'm writing a Shopify-facebook app and i'm struggling to find a practical method to test my code ,since it's all depended on the external APIs ,and the only tests i'm doing is hands-on test (run the app ,check manually if it's working )Mocking the external APIs(Shopify's ) with nock seems to be a time consuming task ,and might end up generating bugs in the mocks

Submitted October 10, 2017 at 11:51PM by 10701220