Fix incorrect assert_redirected_to failure message

In some instances, `assert_redirected_to` assertion was returning an
incorrect and misleading failure message when the assertion failed.
This was due to a disconnect in how the assertion computes the redirect
string for the failure message and how `redirect_to` computes the
string that is actually used for redirection.

I made the `_compute_redirect_to_loaction` method used by `redirect_to`
public and call that from the method `assert_redirect_to` uses to
calculate the URL.

The reveals a new test failure due to the regex used by
`_compute_redirect_to_location` allow `_` in the URL scheme.

1 files changed, 5 insertions, 15 deletions

diff --git a/actionpack/lib/action_dispatch/testing/assertions/response.rb b/actionpack/lib/action_dispatch/testing/assertions/response.rb
index 44ed0ac1f3..93f9fab9c2 100644
--- a/actionpack/lib/action_dispatch/testing/assertions/response.rb
+++ b/actionpack/lib/action_dispatch/testing/assertions/response.rb
@@ -67,21 +67,11 @@ module ActionDispatch
         end
 
         def normalize_argument_to_redirection(fragment)
-          normalized = case fragment
-            when Regexp
-              fragment
-            when %r{^\w[A-Za-z\d+.-]*:.*}
-              fragment
-            when String
-              @request.protocol + @request.host_with_port + fragment
-            when :back
-              raise RedirectBackError unless refer = @request.headers["Referer"]
-              refer
-            else
-              @controller.url_for(fragment)
-            end
-
-          normalized.respond_to?(:delete) ? normalized.delete("\0\r\n") : normalized
+          if Regexp === fragment
+            fragment
+          else
+            @controller._compute_redirect_to_location(fragment)
+          end
         end
     end
   end