app/services/tables/distribution.rb

@@ -7,6 +7,7 @@ module Tables
     def initialize(min_per_table:, max_per_table:)
       @min_per_table = min_per_table
       @max_per_table = max_per_table
+      @tables = []
     end
 
     def random_distribution(people)

spec/services/tables/swap_spec.rb

@@ -0,0 +1,33 @@
+require 'rails_helper'
+
+module Tables
+  RSpec.describe Swap do
+    describe '#each' do
+      let(:initial_solution) do
+        Distribution.new(min_per_table: 2, max_per_table: 2).tap do |distribution|
+          distribution.tables << %i[a b]
+          distribution.tables << %i[c d]
+        end
+      end
+
+      let(:swaps) do
+        acc = []
+        described_class.new(initial_solution).each do |solution|
+          acc << solution.tables.map(&:dup)
+        end
+        acc
+      end
+
+      it 'yields all possible swaps' do
+        expect(swaps.count).to eq(4)
+      end
+
+      it 'swaps the people' do
+        expect(swaps).to include([%i[a d], %i[c b]])
+        expect(swaps).to include([%i[b c], %i[d a]])
+        expect(swaps).to include([%i[a c], %i[d b]])
+        expect(swaps).to include([%i[b d], %i[c a]])
+      end
+    end
+  end
+end