Update type handling in PaymentMethodsController and add tests

app/controllers/spree/admin/payment_methods_controller.rb

@@ -33,7 +33,7 @@ module Spree
 
         invoke_callbacks(:update, :before)
 
-        if @payment_method['type'].to_s != payment_method_class
+        if @payment_method.type.to_s != payment_method_class
           @payment_method.update_columns(
             type: payment_method_class,
             updated_at: Time.zone.now
@@ -97,7 +97,7 @@ module Spree
       private
 
       def payment_method_class
-        base_params.delete(:type)
+        @payment_method_class ||= base_params.delete(:type)
       end
 
       def force_environment

spec/controllers/spree/admin/payment_methods_controller_spec.rb

@@ -81,6 +81,23 @@ module Spree
           expect(payment_method.calculator.preferred_amount).to eq 456
           expect(payment_method.calculator.preferred_currency).to eq "GBP"
         end
+
+        context "when the given payment method type does not match" do
+          let(:params) {
+            {
+              id: payment_method.id,
+              payment_method: {
+                type: "Spree::Gateway::Bogus"
+              }
+            }
+          }
+
+          it "updates the payment method type" do
+            spree_post :update, params
+
+            expect(PaymentMethod.find(payment_method.id).type).to eq "Spree::Gateway::Bogus"
+          end
+        end
       end
 
       context "on a StripeConnect payment method" do