/// <summary>
 /// Prepares a method to make it callable with default values by the ExpressionParser's methods
 /// </summary>
 /// <param name="variables">the variables that are used for the expressioncall</param>
 /// <param name="fixtures">the fixtures coming from the caller that must be used as default-parameters</param>
 public static void PrepareExpressionVariables(IScope variables, Dictionary <string, object> fixtures)
 {
     foreach (KeyValuePair <string, MethodInfo> method in expressionMethods)
     {
         InvokationHelper helper = DefaultParameterAttribute.GenerateHelper(method.Value, fixtures);
         if (helper != null)
         {
             variables[method.Key] = helper;
         }
     }
 }