Should #helpers be class_eval-ing the passed in mod?

 def helpers(new_mod = nil, &block)
          if block_given? || new_mod
            mod = new_mod || Module.new
            define_boolean_in_mod(mod)
            inject_api_helpers_to_mod(mod) if new_mod

            inject_api_helpers_to_mod(mod) do
              mod.class_eval(&block)
            end if block_given?

            namespace_stackable(:helpers, mod)
          else
            mod = Module.new
            namespace_stackable(:helpers).each do |mod_to_include|
              mod.send :include, mod_to_include
            end
            change!
            mod
          end
        end

mod could be new_mod which means it is having methods injected into it. If you assign something like helpers Some::Poor::ExternalModule it now will get methods included into it from the block due to the mod.class_eval(&block).

Is that correct? This doesn't seem like a side-effect we would want.

Start with the helpers method shown in the issue and trace how new_mod, inject_api_helpers_to_mod, and mod.class_eval interact. Reproduce the behavior with an external module passed to helpers alongside a block, then determine whether modifying that module is intended. Done means the expected behavior is decided and the implementation or regression coverage reflects it.