Add with_default_charset helper.

actionpack/test/controller/content_type_test.rb

@@ -68,12 +68,11 @@ def test_render_defaults
   end
 
   def test_render_changed_charset_default
-    ActionDispatch::Response.default_charset = "utf-16"
-    get :render_defaults
-    assert_equal "utf-16", @response.charset
-    assert_equal Mime::HTML, @response.content_type
-  ensure
-    ActionDispatch::Response.default_charset = "utf-8"
+    with_default_charset "utf-16" do
+      get :render_defaults
+      assert_equal "utf-16", @response.charset
+      assert_equal Mime::HTML, @response.content_type
+    end
   end
 
   # :ported:
@@ -105,12 +104,11 @@ def test_nil_charset_from_body
   end
 
   def test_nil_default_for_erb
-    ActionDispatch::Response.default_charset = nil
-    get :render_default_for_erb
-    assert_equal Mime::HTML, @response.content_type
-    assert_nil @response.charset, @response.headers.inspect
-  ensure
-    ActionDispatch::Response.default_charset = "utf-8"
+    with_default_charset nil do
+      get :render_default_for_erb
+      assert_equal Mime::HTML, @response.content_type
+      assert_nil @response.charset, @response.headers.inspect
+    end
   end
 
   def test_default_for_erb
@@ -130,6 +128,16 @@ def test_change_for_builder
     assert_equal Mime::HTML, @response.content_type
     assert_equal "utf-8", @response.charset
   end
+
+  private
+
+  def with_default_charset(charset)
+    old_default_charset = ActionDispatch::Response.default_charset
+    ActionDispatch::Response.default_charset = charset
+    yield
+  ensure
+    ActionDispatch::Response.default_charset = old_default_charset
+  end
 end
 
 class AcceptBasedContentTypeTest < ActionController::TestCase