diff --git a/.tool-versions b/.tool-versions
new file mode 100644
index 0000000..05913ea
--- /dev/null
+++ b/.tool-versions
@@ -0,0 +1 @@
+ruby 4.0.6
diff --git a/README.md b/README.md
index fdd13d2..a70a459 100644
--- a/README.md
+++ b/README.md
@@ -1,5 +1,18 @@
 # Ruby Technical Test
 
+## Dependencies
+
+* Ruby 4.0.6
+* Minitest 6.0.6
+
+## Instructions
+
+Checkout class is in `checkout.rb`
+
+Run tests with `ruby -Ilib:test tests.rb`
+
+`main.rb` is a scratchpad
+
 ## Initial Thoughts
 
 * Cart can be stored in an array of strings
diff --git a/checkout.rb b/checkout.rb
new file mode 100644
index 0000000..bae0ff4
--- /dev/null
+++ b/checkout.rb
@@ -0,0 +1,28 @@
+class Checkout
+  class InvalidItem < StandardError; end
+
+  AVAILABLE_ITEMS = {
+    PI5: 60.00,
+    ZERO2W: 15.00,
+    PICO2: 4.00
+  }
+
+  def initialize
+    @items = []
+  end
+
+  def add(item)
+    raise InvalidItem unless valid_item(item)
+    @items.push item
+  end
+
+  def items
+    @items
+  end
+
+  private
+
+  def valid_item(item)
+    return AVAILABLE_ITEMS.keys.include?(item)
+  end
+end
\ No newline at end of file
diff --git a/main.rb b/main.rb
new file mode 100644
index 0000000..93acc16
--- /dev/null
+++ b/main.rb
@@ -0,0 +1,9 @@
+require "./checkout.rb"
+
+checkout = Checkout.new()
+
+checkout.add(:PI5)
+checkout.add(:ZERO2W)
+
+checkout.items # ["PI5", "ZERO2W"]
+checkout.total # 75.00
diff --git a/tests.rb b/tests.rb
new file mode 100644
index 0000000..e5c422e
--- /dev/null
+++ b/tests.rb
@@ -0,0 +1,22 @@
+require "minitest/autorun"
+
+require "./checkout.rb"
+
+class TestCheckout < Minitest::Test
+  def setup
+    @checkout = Checkout.new
+  end
+
+  def test_that_unknown_items_cannot_be_added
+    assert_raises Checkout::InvalidItem do
+      @checkout.add(:foo)
+    end
+  end
+
+  def test_that_allowed_items_are_added
+    @checkout.add(:PI5)
+    @checkout.add(:ZERO2W)
+
+    assert_equal [:PI5, :ZERO2W].sort, @checkout.items.sort
+  end
+end
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