Add forgotten testcase

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@4159 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

activesupport/test/core_ext/pathname_test.rb

+require 'test/unit'
+require File.dirname(__FILE__) + '/../../lib/active_support/core_ext/pathname'
+
+class TestPathname < Test::Unit::TestCase
+  
+  def test_clean_within
+    assert_equal "Hi", Pathname.clean_within("Hi")
+    assert_equal "Hi", Pathname.clean_within("Hi/a/b/../..")
+    assert_equal "Hello\nWorld", Pathname.clean_within("Hello/a/b/../..\na/b/../../World/c/..")
+  end
+  
+end