feat: serialize error payloads

Author: gabeodess

.gitignore

@@ -56,3 +56,4 @@ Gemfile.lock
 # Used by RuboCop. Remote config files pulled in from inherit_from directive.
 .rubocop_cache
 # .rubocop-https?--*
+.idea

lib/leopard/message_wrapper.rb

@@ -39,7 +39,7 @@ def respond(payload)
       #
       # @return [void]
       def respond_with_error(err, &)
-        raw.respond_with_error(err, &)
+        raw.respond_with_error(err.is_a?(Exception) ? err : serialize(err), &)
       end
 
       private

test/lib/message_wrapper.rb

@@ -75,11 +75,11 @@ def respond_with_error(err)
     assert_equal [err], msg.error_args
   end
 
-  it 'passes hash payloads through when responding with error' do
+  it 'serializes hash payloads when responding with error' do
     err = { 'description' => 'broken', 'code' => 422 }
     wrapper.respond_with_error(err)
 
-    assert_equal [err], msg.error_args
+    assert_equal ['{"description":"broken","code":422}'], msg.error_args
   end
 
   it 'forwards blocks when responding with error' do