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 +1,83 @@
+require 'rails_helper'
+
+module Tables
+  RSpec.describe Swap do
+    describe '#each' do
+      let(:swaps) do
+        acc = []
+        described_class.new(initial_solution).each do |solution|
+          acc << solution.tables.map(&:dup)
+        end
+        acc
+      end
+
+      context 'when there are two tables with two people 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
+
+        it 'yields all possible swaps between the tables' do
+          expect(swaps).to contain_exactly(
+            [%i[a d], %i[c b]],
+            [%i[b c], %i[d a]],
+            [%i[a c], %i[d b]],
+            [%i[b d], %i[c a]]
+          )
+        end
+      end
+
+      context 'when there are two tables with three people each' do
+        let(:initial_solution) do
+          Distribution.new(min_per_table: 3, max_per_table: 3).tap do |distribution|
+            distribution.tables << %i[a b c]
+            distribution.tables << %i[d e f]
+          end
+        end
+
+        it 'yields all possible swaps between the tables' do
+          expect(swaps).to contain_exactly(
+            [%i[b c d], %i[e f a]],
+            [%i[b c e], %i[f d a]],
+            [%i[b c f], %i[d e a]],
+            [%i[c a d], %i[e f b]],
+            [%i[c a e], %i[f d b]],
+            [%i[c a f], %i[d e b]],
+            [%i[a b d], %i[e f c]],
+            [%i[a b e], %i[f d c]],
+            [%i[a b f], %i[d e c]]
+          )
+        end
+      end
+
+      context 'when there are three tables with two people 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]
+            distribution.tables << %i[e f]
+          end
+        end
+
+        it 'yields all possible swaps between the tables' do
+          expect(swaps).to contain_exactly(
+            [%i[b c], %i[d a], %i[e f]],
+            [%i[b d], %i[c a], %i[e f]],
+            [%i[a c], %i[d b], %i[e f]],
+            [%i[a d], %i[c b], %i[e f]],
+            [%i[b e], %i[c d], %i[f a]],
+            [%i[b f], %i[c d], %i[e a]],
+            [%i[a e], %i[c d], %i[f b]],
+            [%i[a f], %i[c d], %i[e b]],
+            [%i[a b], %i[d e], %i[f c]],
+            [%i[a b], %i[d f], %i[e c]],
+            [%i[a b], %i[c e], %i[f d]],
+            [%i[a b], %i[c f], %i[e d]]
+          )
+        end
+      end
+    end
+  end
+end