One improvement that was suggested to me earlier, is to calculate the hash straight in the test to demonstrate what's happening, as opposed to having a magic digest string hardcoded ([example](https://github.com/Shopify/active_merchant/blob/2d7aadf6d5578e20d360bb984b5eaeb332502146/test/unit/integrations/paydollar_module_test.rb#L29-L32)).