Run the logger tests in isolation

activesupport/lib/active_support/testing/isolation.rb

@@ -39,7 +39,7 @@ class ParallelEach
         include Enumerable
 
         # default to 2 cores
-        CORES = ENV['TEST_CORES'].to_i || 2
+        CORES = (ENV['TEST_CORES'] || 2).to_i
 
         def initialize list
           @list  = list

railties/test/application/rack/logger_test.rb

@@ -5,6 +5,7 @@
 module ApplicationTests
   module RackTests
     class LoggerTest < ActiveSupport::TestCase
+      include ActiveSupport::Testing::Isolation
       include ActiveSupport::LogSubscriber::TestHelper
       include Rack::Test::Methods
 
@@ -17,6 +18,7 @@ def setup
       end
 
       def teardown
+        super
         teardown_app
       end