Extract a DiscomfortCalculator class

app/services/tables/discomfort_calculator.rb

@@ -0,0 +1,22 @@
+module Tables
+  class DiscomfortCalculator
+    private attr_reader :table
+    def initialize(table)
+      @table = table
+    end
+
+    def calculate
+      group_merging
+    end
+
+    private
+
+    def group_merging
+      10 * (number_of_groups - 1)
+    end
+
+    def number_of_groups
+      table.map(&:affinity_groups).flatten.uniq.count
+    end
+  end
+end

app/services/tables/distribution.rb

@@ -1,3 +1,5 @@
+require_relative '../../extensions/tree_node_extension'
+
 module Tables
   class Distribution
     attr_accessor :tables
@@ -56,11 +58,7 @@ module Tables
     private
 
     def local_discomfort(table)
-      10 * (number_of_groups(table) - 1)
-    end
-
-    def number_of_groups(table)
-      table.map(&:affinity_groups).flatten.uniq.count
+      DiscomfortCalculator.new(table).calculate
     end
   end
 end

spec/services/tables/discomfort_calculator_spec.rb

@@ -1,10 +1,8 @@
 require 'rails_helper'
-
 module Tables
-  RSpec.describe Distribution do
-    describe '#local_discomfort' do
-      let(:service) { described_class.new(min_per_table: 5, max_per_table: 5) }
-      before { service.tables = [table] }
+  RSpec.describe DiscomfortCalculator do
+    describe '#group_merging' do
+      let(:calculator) { described_class.new(table) }
 
       context 'when there is just one group in the table' do
         let(:table) do
@@ -14,7 +12,7 @@ module Tables
           end
         end
 
-        it { expect(service.send(:local_discomfort, table)).to eq(0) }
+        it { expect(calculator.send(:group_merging)).to eq(0) }
       end
 
       context 'when the table contains two groups' do
@@ -26,7 +24,7 @@ module Tables
           guests.each(&:save!)
         end
 
-        it { expect(service.send(:local_discomfort, table)).to eq(10) }
+        it { expect(calculator.send(:group_merging)).to eq(10) }
       end
 
       context 'when the table contains three groups' do
@@ -38,7 +36,7 @@ module Tables
           guests.each(&:save!)
         end
 
-        it { expect(service.send(:local_discomfort, table)).to eq(20) }
+        it { expect(calculator.send(:group_merging)).to eq(20) }
       end
     end
   end