2 files changed, 20 insertions, 2 deletions
diff --git a/activesupport/lib/active_support/testing/isolation.rb b/activesupport/lib/active_support/testing/isolation.rb
index 090e0c5c89..dd13abcd5d 100644
--- a/activesupport/lib/active_support/testing/isolation.rb
+++ b/activesupport/lib/active_support/testing/isolation.rb
@@ -21,6 +21,11 @@ module ActiveSupport::Testing
     end
 
     def run(result)
+      unless defined?(@@ran_class_setup)
+        self.class.setup
+        @@ran_class_setup = true
+      end
+
       yield(Test::Unit::TestCase::STARTED, name)
 
       @_result = result
diff --git a/activesupport/test/isolation_test.rb b/activesupport/test/isolation_test.rb
index b844bbb673..5a1f285476 100644
--- a/activesupport/test/isolation_test.rb
+++ b/activesupport/test/isolation_test.rb
@@ -5,6 +5,12 @@ if ENV['CHILD']
   class ChildIsolationTest < ActiveSupport::TestCase
     include ActiveSupport::Testing::Isolation
 
+    def self.setup
+      File.open(File.join(File.dirname(__FILE__), "fixtures", "isolation_test"), "a") do |f|
+        f.puts "hello"
+      end
+    end
+
     def setup
       @instance = "HELLO"
     end
@@ -64,6 +70,8 @@ if ENV['CHILD']
 else
   class ParentIsolationTest < ActiveSupport::TestCase
 
+    File.open(File.join(File.dirname(__FILE__), "fixtures", "isolation_test"), "w") {}
+
     ENV["CHILD"] = "1"
     OUTPUT = `#{Gem.ruby} -I#{File.dirname(__FILE__)} #{File.expand_path(__FILE__)} -v`
     ENV.delete("CHILD")
@@ -131,12 +139,17 @@ else
 
     test "backtrace is printed for errors" do
       assert_equal 'Error', @backtraces["test_captures_errors"][:type]
-      assert_match %{isolation_test.rb:21:in `test_captures_errors'}, @backtraces["test_captures_errors"][:output]
+      assert_match %r{isolation_test.rb:\d+:in `test_captures_errors'}, @backtraces["test_captures_errors"][:output]
     end
 
     test "backtrace is printed for failures" do
       assert_equal 'Failure', @backtraces["test_captures_failures"][:type]
-      assert_match %{isolation_test.rb:25:in `test_captures_failures'}, @backtraces["test_captures_failures"][:output]
+      assert_match %r{isolation_test.rb:\d+:in `test_captures_failures'}, @backtraces["test_captures_failures"][:output]
+    end
+
+    test "self.setup is run only once" do
+      text = File.read(File.join(File.dirname(__FILE__), "fixtures", "isolation_test"))
+      assert_equal "hello\n", text
     end
 
   end