feature: add horizontal move class

lib/move/horizontal.rb

@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+module Move
+  # unlimited horizontal movement for a piece
+  class Horizontal
+    def unhindered_legal_end_positions(position)
+      position = Position.parse(position) if position.is_a? String
+      letters = ("A".."H").to_a - [position.letter]
+      letters.map { |l| Position.new(l, position.number) }
+    end
+  end
+end

main.rb

@@ -3,3 +3,5 @@
 require_relative 'lib/board'
 require_relative 'lib/position'
 require_relative 'lib/piece'
+
+require_relative 'lib/move/horizontal'

test/move/horizontal_test.rb

@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+require "minitest/autorun"
+
+module Move
+  class HorizontalTest < Minitest::Test
+    def test_returns_unhindered_positions
+      move = Move::Horizontal.new
+
+      legal_end_positions = %w[A3 B3 C3 E3 F3 G3 H3].map { |p| Position.parse(p) } # without D4
+      assert_equal  legal_end_positions, move.unhindered_legal_end_positions("D3")
+    end
+  end
+end