Update conditional argument handling to correctly support lambdas

Author: yjukaku

lib/workflow/event.rb

@@ -28,9 +28,13 @@ def condition_applicable?(object, event_arguments)
             object.send(condition, *event_arguments)
           end
         else
-          # since blocks can ignore extra arguments without raising an error in Ruby,
-          # no `if` is needed - compare with `arity` switch in above methods handling
-          condition.call(object, *event_arguments)
+          # Blocks and non-lambda Procs can ignore extra arguments without raising an error in Ruby,
+          # but lambdas cannot, so we still have to check arity
+          if condition.arity == 1 # no additional parameters accepted
+            condition.call(object)
+          else
+            condition.call(object, *event_arguments)
+          end
         end
       else
         true

test/conditionals_test.rb

@@ -92,7 +92,8 @@ def check_low_battery?() # supports no arguments, lets test below, what happens
           event :turn_on, :transitions_to => :low_battery # otherwise
         end
         state :on do
-          event :check, :transitions_to => :low_battery, :if => proc { |obj| return false }
+          # Use a lambda proc, which enforces correct arity
+          event :check, :transitions_to => :low_battery, :if => -> (obj) { return false }
           event :check, :transitions_to => :on # stay in on state otherwise
         end
         state :low_battery