.NET core supermarket pricing kata
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.NET core supermarket pricing kata



We’re going to see how far we can get in implementing a supermarket checkout that calculates the total price of a number of items. In a normal supermarket, things are identified using Stock Keeping Units, or SKUs. In our store, we’ll use individual letters of the alphabet (A, B, C, and so on). Our goods are priced individually. In addition, some items are multipriced: buy n of them, and they’ll cost you y pounds. For example, item ‘A’ might cost 50 pounds individually, but this week we have a special offer: buy three ‘A’s and they’ll cost you 130. The price and offer table:

Item  Price   Offer
A     50       3 for 130
B     30       2 for 45
C     20
D     15

Our checkout accepts items in any order, so that if we scan a B, an A, and another B, we’ll recognize the two B’s and price them at 45 (for a total price so far of 95).

Getting Started

The interface to your checkout can be anything you like but we’d suggest passing in a string of SKUs to begin with. Here are the first few tests from a Ruby implementation, but feel free to use any language, and write the tests in any order you prefer:

def price(goods)
   co = CheckOut.new(RULES)
   goods.split(//).each { |item| co.scan(item) }

def test_totals
  assert_equal(  0, price(""))
  assert_equal( 50, price("A"))
  assert_equal( 80, price("AB"))
  assert_equal(115, price("CDBA"))
  assert_equal(100, price("AA"))
  assert_equal(130, price("AAA"))
  assert_equal(175, price("AAABB"))

credits: adapted from Dave Thomas http://codekata.pragprog.com/2007/01/kata_nine_back_.html

Build and Run

To build the kata, navigate to src/Kata.Checkout and run the following commands:

dotnet restore
dotnet build

To run the tests, navigate to the tests/Kata.Checkout.Tests directory and type the following commands:

dotnet restore
dotnet build
dotnet test

You must run dotnet restore in the src/Kata.Checkout directory before you can run the tests. dotnet build will follow the dependency and build both the library and unit tests projects, but it will not restore NuGet packages.


The project uses dotnet-watch as file watcher for dotnet that restarts the application when changes in the source code are detected. For continuous test running, just launch

dotnet watch test