prevent formater loader registering duplicate listeners

Author: JonRowe

lib/rspec/core/formatters.rb

@@ -143,9 +143,11 @@ def add(formatter_to_use, *paths)
 
       if !Loader.formatters[formatter_class].nil?
         formatter = formatter_class.new(*args)
+        return formatter if duplicate_formatter_exists?(formatter)
         @reporter.register_listener formatter, *notifications_for(formatter_class)
       elsif defined?(RSpec::LegacyFormatters)
         formatter = RSpec::LegacyFormatters.load_formatter formatter_class, *args
+        return formatter if duplicate_formatter_exists?(formatter)
         @reporter.register_listener formatter, *formatter.notifications
       else
         call_site = "Formatter added at: #{::RSpec::CallerFilter.first_non_rspec_line}"
@@ -163,7 +165,7 @@ def add(formatter_to_use, *paths)
         WARNING
         return
       end
-      @formatters << formatter unless duplicate_formatter_exists?(formatter)
+      @formatters << formatter
       formatter
     end
 

spec/rspec/core/formatters_spec.rb

@@ -117,6 +117,7 @@ module RSpec::Core::Formatters
         before { loader.add :documentation, output }
 
         it "doesn't add the formatter for the same output target" do
+          expect(reporter).to_not receive(:register_listener)
           expect {
             loader.add :documentation, output
           }.not_to change { loader.formatters.length }