diff --git a/app/services/vns/engine.rb b/app/services/vns/engine.rb
index 5408bc9..6a68eaf 100644
--- a/app/services/vns/engine.rb
+++ b/app/services/vns/engine.rb
@@ -13,6 +13,10 @@ module VNS
       end
     end
 
+    def initialize
+      @perturbations = Set.new
+    end
+
     def target_function(&function)
       @target_function = function
     end
@@ -23,7 +27,6 @@ module VNS
     end
 
     def add_perturbation(klass)
-      @perturbations ||= Set.new
       @perturbations << klass
     end
 
@@ -38,11 +41,7 @@ module VNS
     attr_writer :initial_solution
 
     def run
-      raise 'No target function defined' unless @target_function
-      raise 'No optimizations defined' unless @optimizations
-      raise 'No initial solution defined' unless @initial_solution
-
-      @perturbations ||= Set.new
+      check_preconditions!
 
       @current_solution = @initial_solution
       @best_score = @target_function.call(@current_solution)
@@ -77,6 +76,12 @@ module VNS
 
     private
 
+    def check_preconditions!
+      raise 'No target function defined' unless @target_function
+      raise 'No optimizations defined' unless @optimizations
+      raise 'No initial solution defined' unless @initial_solution
+    end
+
     def run_all_optimizations
       self.class.sequence(@optimizations).each do |optimization|
         optimize(optimization)