From e5707839357afa7e955c1ec330ce54971706c4db Mon Sep 17 00:00:00 2001
From: David Underwood <david@unprinted.email>
Date: Tue, 21 Jul 2026 09:48:32 -0400
Subject: [PATCH] Add Shop class to keep track of available products

---
 shop.rb           | 22 ++++++++++++++++++++++
 test/shop_test.rb | 25 +++++++++++++++++++++++++
 2 files changed, 47 insertions(+)
 create mode 100644 shop.rb
 create mode 100644 test/shop_test.rb

diff --git a/shop.rb b/shop.rb
new file mode 100644
index 0000000..4d29ff9
--- /dev/null
+++ b/shop.rb
@@ -0,0 +1,22 @@
+class Shop
+  class DuplicateProductIdError < StandardError; end
+  def initialize
+    @products = []
+  end
+
+  def products
+    @products
+  end
+
+  def add_product(product)
+    raise DuplicateProductIdError if duplicate_id?(product.id)
+
+    @products.push(product)
+  end
+
+  private
+
+  def duplicate_id?(id)
+    @products.map(&:id).include?(id)
+  end
+end
diff --git a/test/shop_test.rb b/test/shop_test.rb
new file mode 100644
index 0000000..e9e3dc3
--- /dev/null
+++ b/test/shop_test.rb
@@ -0,0 +1,25 @@
+require "minitest/autorun"
+
+require "shop.rb"
+require "product.rb"
+
+class ShopTest < Minitest::Test
+  def setup
+    @shop = Shop.new
+  end
+
+  def test_adding_a_product
+    pico = Product.new(id: 'PICO2', price: 4.00)
+    @shop.add_product(pico)
+
+    assert_equal [pico], @shop.products
+  end
+
+  def test_duplicate_product_id_raises_an_error
+    @shop.add_product(Product.new(id: 'PICO2'))
+
+    assert_raises Shop::DuplicateProductIdError do
+     @shop.add_product(Product.new(id: 'PICO2'))
+    end
+  end
+end