Updated formatter specs

Author: Sebastián Tello

spec/rspec/core/formatters_spec.rb

@@ -1,5 +1,4 @@
 require 'pathname'
-require 'rspec/core/resources/a_custom_formatter'
 
 module RSpec::Core::Formatters
   RSpec.describe Loader do
@@ -140,11 +139,14 @@ module RSpec::Core::Formatters
       end
 
       context "When a custom formatter exists" do
-        before { loader.add Custom::AGeneralFormatter, output }
+        specific_formatter = RSpec::Core::Formatters::JsonFormatter
+        generic_formatter = specific_formatter.superclass
+
+        before { loader.add generic_formatter, output }
 
         it "adds a subclass of that formatter for the same output target" do
           expect {
-            loader.add Custom::AMoreSpecificFormatter, output
+            loader.add specific_formatter, output
           }.to change { loader.formatters.length }
         end
       end