I want to build a WooCommerce payment plugin for learning how a payment plugin is built. I don't have a real banking system behind it and I am looking if there is someway to build the plugin and test it without the need of a real system behind it. Does anyone offer a testing payment gateway for free?
Most payment APIs like Braintree give you a sandbox API for testing. You can build your payment plugin on top of those APIs or build one similar to that.