No longer add missing leading / on path args to assert_redirected_to. Deprecated in 2.3.6.

actionpack/lib/action_dispatch/testing/assertions/response.rb

@@ -132,16 +132,21 @@ module ActionDispatch
         end
 
         def normalize_argument_to_redirection(fragment)
-          after_routing = @controller.url_for(fragment)
-          if after_routing =~ %r{^\w+://.*}
-            after_routing
-          else
-            # FIXME - this should probably get removed.
-            if after_routing.first != '/'
-              after_routing = '/' + after_routing
+          case fragment
+          when %r{^\w[\w\d+.-]*:.*}
+            fragment
+          when String
+            if fragment =~ %r{^\w[\w\d+.-]*:.*}
+              fragment
+            else
+              @request.protocol + @request.host_with_port + fragment
             end
-            @request.protocol + @request.host_with_port + after_routing
-          end
+          when :back
+            raise RedirectBackError unless refer = @request.headers["Referer"]
+            refer
+          else
+            @controller.url_for(fragment)
+          end.gsub(/[\r\n]/, '')
         end
 
         def validate_request!

actionpack/test/controller/action_pack_assertions_test.rb

@@ -469,9 +469,11 @@ class ActionPackAssertionsControllerTest < ActionController::TestCase
     assert_redirected_to '/some/path'
   end
 
-  def test_redirected_to_url_no_leadling_slash
+  def test_redirected_to_url_no_leading_slash_fails
     process :redirect_to_path
-    assert_redirected_to 'some/path'
+    assert_raise ActiveSupport::TestCase::Assertion do
+      assert_redirected_to 'some/path'
+    end
   end
 
   def test_redirected_to_url_full_url