   # private
   
   _check_constructor_usage = (expects_method_name) ->
-    fail(messages.ExpectsMethodAlreadyExists, expects_method_name) unless not Object.prototype[ expects_method_name ]?
+    fail(messages.ExpectsMethodAlreadyExists, expects_method_name) if Object.prototype[ expects_method_name ]?
     
   _install_expects_method = (expects_method_name) ->
     Object.prototype[ expects_method_name ] = (method_name) ->

      ( @_args.every ( element, i ) -> element == args[ i ] )

  find_errors: ->
    if not @_called then format(messages.ExpectationNeverCalled, @_method_name, @_args) else ""

  # private


  throw new Error(format(message, args...))

#  
# From http://stackoverflow.com/questions/9880578/coffeescript-version-of-string-format-sprintf-etc-for-javascript-or-node-js
#
format = (message, args...) ->    # format("{0} + {1} = {2}", 2, 2, "four") => "2 + 2 = four"
  message.replace /{(\d)+}/g, (match, i) ->
