When the request.remote_addr remains the default for testing, which is 0.0.0.0, the exception is simply raised inline (bystepping the regular exception handling from rescue_action). If the request.remote_addr is anything else, the regular rescue_action process takes place. This means you can test your rescue_action code by setting remote_addr to something else than 0.0.0.0.
The exception is stored in the exception accessor for further inspection.
# File actionpack/lib/action_controller/test_case.rb, line 135 135: def self.included(base) 136: base.class_eval do 137: attr_accessor :exception 138: protected :exception, :exception= 139: end 140: end