Added another test (will squash later)

spec/aws_sns_action_spec.rb

@@ -11,14 +11,33 @@
             aws_sns_client: aws_sns_client,
             platform: 'FCM',
             platform_name: 'FCM_SNS_PLATFORM_APP',
-            platform_fcm_server_key: 'PLACEHOLDER_FCM_KEY',
-            attributes_override: {}
+            platform_fcm_server_key: 'PLACEHOLDER_FCM_KEY'
           })
         end
         ").runner.execute(:test)
 
         expect(result).to eq("String")
       end
+
+      it 'raises an error if no AWS client can be created' do
+        expect do
+          Fastlane::FastFile.new.parse("
+            lane :test do
+
+              # Just in case they are set
+              ENV.delete('AWS_SNS_ACCESS_KEY')
+              ENV.delete('AWS_SNS_SECRET_ACCESS_KEY')
+              ENV.delete('AWS_SNS_REGION')
+
+              arn = aws_sns({
+                platform: 'FCM',
+                platform_name: 'FCM_SNS_PLATFORM_APP',
+                platform_fcm_server_key: 'PLACEHOLDER_FCM_KEY'
+              })
+            end
+          ").runner.execute(:test)
+        end.to raise_error(FastlaneCore::Interface::FastlaneError)
+      end
     end
   end
 end