Hello everyone, we are developing the first extension app for the Shopify platform. The main functions are completed, but now we have encountered a problem. We need to test whether the payment function is normal. How should we test it?
What does payment function mean? And what do you mean by normal?
Do you mean you have written a Shopify functions relating to payments? Or you want to test how your Shopify app handles when merchants subscribe to your app?
Yes, I want to test how my Shopify app handles when merchants subscribe to my app.
You can do some on a partner development store. Then you install the app and your app should take you through the usual flow but with a test payment, everything else should work the same 
If you are using managed billing this will happen automatically, if you’ve added payments via GraphQL ensure you mark them as test payments for your dev store
Using Shopify test payment
https://help.shopify.com/en/manual/payments/shopify-payments/testing-shopify-payments
Also you can add param test=true when using appsubscriptioncreate GraphQL mutation