Fix a timezone test failure.

test/liquid/standard_filter_test.rb

@@ -157,9 +157,11 @@ class StandardFiltersTest < Test::Unit::TestCase
 
     assert_equal nil, @filters.date(nil, "%B")
 
+    with_timezone("UTC") do
       assert_equal "07/05/2006", @filters.date(1152098955, "%m/%d/%Y")
       assert_equal "07/05/2006", @filters.date("1152098955", "%m/%d/%Y")
     end
+  end
 
 
   def test_first_last
@@ -248,4 +250,14 @@ class StandardFiltersTest < Test::Unit::TestCase
   def test_cannot_access_private_methods
     assert_template_result('a',"{{ 'a' | to_number }}")
   end
+
+  private
+
+  def with_timezone(tz)
+    old_tz = ENV['TZ']
+    ENV['TZ'] = tz
+    yield
+  ensure
+    ENV['TZ'] = old_tz
+  end
 end # StandardFiltersTest