Stub instance method :backtrace, insted of defining it

spec/google/apis/errors_spec.rb

@@ -80,10 +80,8 @@ RSpec.describe Google::Apis::Error do
 
     context '@cause is falsy' do
       before do
-        subject.class.superclass.class_eval do
+        subject.class.superclass.any_instance.stub(:backtrace) do
-          def backtrace
+          "super class's #backtrace called"
-            "super class's #backtrace called"
-          end
         end
       end