Add BulkDiscount

test/bulk_discount_test.rb

@@ -0,0 +1,15 @@
+require "minitest/autorun"
+
+require 'bulk_discount.rb'
+
+class BulkDiscountTest < Minitest::Test
+  def test_appropriate_discount_is_applied
+    unit_discount = 0.75
+
+    discount = BulkDiscount.new(unit_discount: unit_discount, trigger_quantity: 4)
+
+    assert_equal 0.00, discount.discount_for_quantity(3)
+    assert_equal unit_discount * 4, discount.discount_for_quantity(4)
+    assert_equal unit_discount * 5, discount.discount_for_quantity(5)
+  end
+end