diff --git a/actionpack/lib/action_controller/test_case.rb b/actionpack/lib/action_controller/test_case.rb
index 15e587bcea..4d2a3c712b 100644
--- a/actionpack/lib/action_controller/test_case.rb
+++ b/actionpack/lib/action_controller/test_case.rb
@@ -579,6 +579,7 @@ module ActionController
       #   (<tt>application/x-www-form-urlencoded</tt> or <tt>multipart/form-data</tt>).
       # - +session+: A hash of parameters to store in the session. This may be +nil+.
       # - +flash+: A hash of parameters to store in the flash. This may be +nil+.
+      # - +format+: Request format. Defaults to +nil+. Can be string or symbol.
       #
       # Example calling +create+ action and sending two params:
       #