Introduce specs for the method Tables::DiscomfortCalculator#cohesion_penalty

spec/services/tables/discomfort_calculator_spec.rb

@@ -73,5 +73,63 @@ module Tables
         it { expect(calculator.send(:table_size_penalty)).to eq(10) }
       end
     end
+
+    describe '#cohesion_penalty' do
+      let(:calculator) { described_class.new(table:, hierarchy:) }
+      let(:table) { Table.new(guests) }
+
+      context 'when all guests belong to the same group' do
+        let(:guests) { create_list(:guest, 6, group: family) }
+        let(:hierarchy) { instance_double(AffinityGroupsHierarchy, discomfort: 0) }
+
+        it 'returns 0 as cohesion penalty' do
+          expect(calculator.send(:cohesion_penalty)).to eq(0)
+        end
+      end
+
+      context 'when guests belong to two different groups with discomfort 1' do
+        let(:guests) do
+          create_list(:guest, 3, group: family) +
+            create_list(:guest, 3, group: friends)
+        end
+        let(:hierarchy) do
+          instance_double(AffinityGroupsHierarchy, discomfort: 1)
+        end
+
+        it 'calculates the correct cohesion penalty' do
+          # 3 from family, 3 from friends: 3*3*1 = 9 discomfort
+          expect(calculator.send(:cohesion_penalty)).to eq(10 * (9.0 / 6))
+        end
+      end
+
+      context 'when guests belong to three groups with different discomforts' do
+        let(:guests) do
+          create_list(:guest, 2, group: family) +
+            create_list(:guest, 2, group: friends) +
+            create_list(:guest, 2, group: work)
+        end
+        let(:hierarchy) do
+          instance_double(AffinityGroupsHierarchy)
+        end
+
+        before do
+          allow(hierarchy).to receive(:discomfort).with(family.id, friends.id).and_return(0.5)
+          allow(hierarchy).to receive(:discomfort).with(family.id, work.id).and_return(1)
+          allow(hierarchy).to receive(:discomfort).with(friends.id, work.id).and_return(0.2)
+          allow(hierarchy).to receive(:discomfort).with(friends.id, family.id).and_return(0.5)
+          allow(hierarchy).to receive(:discomfort).with(work.id, family.id).and_return(1)
+          allow(hierarchy).to receive(:discomfort).with(work.id, friends.id).and_return(0.2)
+        end
+
+        it 'calculates the correct cohesion penalty' do
+          # pairs: (family, friends): 2*2*0.5 = 2
+          #        (family, work):    2*2*1   = 4
+          #        (friends, work):   2*2*0.2 = 0.8
+          # total discomfort = 2 + 4 + 0.8 = 6.8
+
+          expect(calculator.send(:cohesion_penalty)).to eq(10 * (6.8 / 6))
+        end
+      end
+    end
   end
 end