Inspired from Supermarket Kata.
- Kata Supermarket
In Jet Supermarket we have a checkout system that can do only one kind of offer, based on quantity of the same item (e.g., 1 apple for 50 cents, 3 apples for 1.30 dollars). At the moment items are priced individually in cents (e.g., 1 apple costs 50 cents), while some items are multi-priced: buy x of them, and they’ll cost you n cents.
The current prices are:
| Item | Unit Price | Special Price |
|---|---|---|
| apple | 50 | 3 for 130 |
| pear | 30 | 2 for 45 |
| pineapple | 220 | |
| banana | 60 |
Our checkout system accepts items in any order, so that if we scan a pear, a pineapple,
and another pear, we’ll recognize the two pears' offer and price them at 45 cents
(for a total price so far of 265 cents).
Because the pricing changes frequently, we want to provide a set of pricing rules
each time we start handling a checkout transaction.
Start making the system able to check an individual price: for now, the cashier will calculate discounts by hand.
Then start implementing offers.
Let's start with apples.
As a cashier,
I want a basic checkout system
so I can let my customers pay for apples* When I checkout an apple, the system charges 50 cents
* When I checkout 3 apples, the system charges 150 centsImplement individual price for other fruits in list: pear, pineapple, banana.
No offers implemented, yet.
As a cashier,
I want to add pear, pineapple and banana to the checkout system
so I can speed up the payment process* When I checkout 1 pear, the system charges 30 cents
* When I checkout 1 pineapple, the system charges 220 cents
* When I checkout 1 banana, the system charges 60 cents
* When I checkout 2 pears, the system charges 60 cents
* When I checkout 2 pineapples, the system charges 440 cents
* When I checkout 2 bananas, the system charges 120 centsTime to implement offers!
As a cashier,
I want to specify offers for items
so my customers will pay less for multiple items purchase* When I checkout 3 apples, the system charges 130 cents instead of 150
* When I checkout 2 pears, the system charges 45 cents instead of 60
* When I checkout 2 pineapples, the system charges 440 cents, as there are no offers for pineapplesTake 3 pay offer.
As a cashier,
I want to add a "take 3 pay 2 offer" kind for items
so my customers will pay less for multiple items purchaseFor the first step, I only want to apply this offers for oranges:
* When I checkout 1 orange, the system charges 45
* When I checkout 3 oranges, the system charges 90 cents instead of 135
* When I checkout 4 oranges, the system charges 135 cents instead of 180
* When I checkout 6 oranges, the system charges 180 cents instead of 270Combo offers.
As a cashier,
I want to specify this offer: 4 apples, 2 pears, 2 bananas and 1 pineapple for 500
so my customers can make delicious fruit salads :)* When I checkout EXACTLY 4 apples, 2 pears, 2 bananas and 1 pineapple, the system charges 500
* All other offers and base prices remains in place
* When I checkout 8 apples, 4 pears, 4 bananas and 2 pineapple, the system charges 1000
* When I checkout 5 apples, 3 pears, 3 bananas and 2 pineapple, the system charges 860 (500+50+30+220+60)
* When I checkout 7 apples, 2 pears, 2 bananas and 1 pineapple, the system charges 630 (500+130)Feel free to go on adding more complex features.
Here some inspiration :)
Let's add some payments features.
As a cashier,
I want a display facing the customer (let's call it 'customer-display')
so that (s)he can see what the total to be paid is* E.g: If customer buys 1 apple (50 cents), on checkout the cash register will tell on the customer-display
| Total: 50 |In this scenario, we have just discovered there is a customer-display we can attach to the cash register.
The customer-display is a pluggable external device.
For the sake of simplicity, in this exercise the customer-display prints its messages to the console.
As a cashier,
I want the cash register to calculate and show me the change
so I can avoid silly mistakes with my customers during the payments * I want to tell the cash register the amount of cash my customers gives to me, so it can calculate the change.
* E.g: If customer buys 1 apple (50 cents) and gives me a 1$ dollar note, the cash register will tell **on the cashier-display**
| Total: 50 |
| Cash: 100 |
| Change: 50 |In this scenario, we have just discovered there is a cashier-display, too.
The cashier-display is a pluggable external device.
For the sake of simplicity, in this exercise the cashier-display prints its messages to the console.
Time to print some fiscal receipt.
As a cashier,
I want to print the fiscal receipt for sold items
so I can collect money from my customers Scenario 1: customer buys items with and without applied offers
Background:
* I checked out 3 apples for 130 cents instead of 150
* I checked out 2 pears for 45 cents instead of 60
* I checked out 2 pineapples for 440 cents (no offers for pineapples)
* When I close the checkout, a fiscal receipt like this is printed to the console:
|Item | Price |
|-----------|------------------|
| apple | 50x3=~~150~~ 130 |
| pear | 30x2=~~60~~ 45 |
| pineapple | 220x2=440 |
| | |
| TOTAL | **615** |
| | |
| Goodbye! | |Scenario 2: an item is damaged then subtracted form the list
Background:
* I checked out 3 apples for 130 cents instead of 150
* I checked out 2 pears for 45 cents instead of 60
* I checked out 2 pineapples for 440 cents (no offers for pineapples)
* I refund 1 pear
* When I close the checkout, a fiscal receipt like this is printed to the console:
| Item | Price |
|-----------|------------------|
| apple | 50x3=~~150~~ 130 |
| pear | 30x2=~~60~~ 45 |
| pineapple | 220x2=440 |
| ~~pear~~ | ~~30x2=60 45~~ |
| pear | 30x1=30 |
| | |
| TOTAL | **600** |
| | |
| Goodbye! | |Scenario 3: automatic calculation of change
Background:
* I checked out 1 pear for 30 cents
* I close the checkout
* I tell to the customer the total amount
* She gives me a 1 dollar bill
* I enter the received amount in the cash register
* I close the transaction, then a fiscal receipt like this is printed to the console:
| Item | Price |
|-----------|-----------------|
| pear | 30 |
| | |
| TOTAL | 30 |
| --------- | --------------- |
| Received | 100 |
| Change | 70 |
| | |
| Goodbye! | |In this scenario, we have just discovered there is a printer attached to the cash register.
The printer is a pluggable external device.
For the sake of simplicity, in this exercise the printer prints its messages to the console.
What if the customers has a fidelity card? Feel free to add implementation details at runtime (e.g., having a 3rd party serve to check cards validity, check the accumulated balance on the card, etc.)
As a cashier,
I want to give a loyalty card that applies an additional 10% discount to some "fidelity products"
so I can build up the loyalty of my customersScenario 1: Customer with fidelity card
Background:
* Apple is a "fidelity product"
* Customer has fidelity card number 123456 (additional 10% discount)
* There's an offer for apples: 3 apples for 130 cents instead of 150
* There's an offer for pears: 2 pears for 45 cents instead of 60
* I checked out 3 apples
* I checked out 2 pears
* I checked out 2 pineapple
* When I close the checkout, a fiscal receipt like this is printed to the console:
|Item | Price |
|-----------|-----------------------------------------------------------------|
| apple | Base price: 50x3=~~150~~; Offer: ~~130~~; Fidelity: 130-10%=117 |
| pear | Base price: 30x2=~~60~~; Offer: 45 |
| pineapple | Base price: 220x2=440 |
| | |
| TOTAL | **602** |
| | |
| | Fidelity card: 123456 |
| | |
| Goodbye! | |Treat the Fidelity Card service as an external service.
For simplicity, create a mock object implementing the behaviors you decide.
As a cashier,
I want to let my customer pay by credit card * E.g: If customer buys 1 apple (50 cents), on checkout with a valid credit card, the cash register will show on the display:
| 0 - Transaction completed successfully |In this scenario, we have an external service that allows the supermarket to pay by credit card.
This is an external service, we don't own it.
Fortunately, there is an interface that allows us to know how to call it:
namespace KataSupermarket;
/// <summary
/// Credit Card Payment Service
/// </summary>
public interface IPaymentService
{
/// <summary>
/// A cash register must connect to the service before accepting the payment.
/// </summary>
/// <param name="username">The username assigned to the supermarket</param>
/// <param name="password">The password assigned to the supermarket</param>
/// <returns>Result</returns>
/// <example>0 - Connection completed successfully.</example>
/// <example>10 - Invalid username or password.</example>
/// <example>90 - Connection failed. Please try again later.</example>
Result Connect(string username, string password);
/// <summary>
/// This method allows the supermarket to charge the <param name="creditCardNumber"></param> with the specified <param name="totalToPay"></param>.
/// </summary>
/// <param name="creditCardNumber"></param>
/// <param name="totalToPay"></param>
/// <returns>Result</returns>
/// <example>0 - Transaction completed successfully.</example>
/// <example>1 - User not connected.</example>
/// <example>10 - Insufficient funds.</example>
/// <example>20 - Expired credit card.</example>
/// <example>30 - Lost or stolen credit card.</example>
/// <example>40 - Unusual activity.</example>
/// <example>90 - Connection failed. Please try again later.
///</example>
Result AcceptPayment(string creditCardNumber, int totalToPay);
}
/// <summary>
/// The result of an interaction with the Payment Service
/// </summary>
public class Result
{
/// <summary>
/// A code that identifies the interaction result.
/// </summary>
public int StatusCode { get; }
/// <summary> A human readable message.
/// </summary>
public string Message { get; }
public Result(int statusCode, string message)
{
StatusCode = statusCode;
Message = message;
}
}Here some other hints for small variations to the exercise 😃
Now, the supermarket manager thinks that having more items and offers will boost his earnings; so he wants to:
-
add these items:
- mango -> 155 cents
- coconut -> 233 cents
- strawberry -> 120 cents
- orange -> 45 cents
- peach -> 40 cents
-
implement new offers that lets us apply new pricing rules:
- combo offers (e.g., buy 3 apple, and you will obtain an additional pear)
- fidelity card offers
- limited quantity offers (e.g., "you can buy this item at discount price, but max 3 pieces")
-
implements the cash payment system
-
implements the credit card payment system
- the goverment stopped producing 1 and 2 cents coins; every bill/invoice has to be rounded to the nearest multiple of 5, even if paid with debet/credit card
- we have to manage the cancellation of a product, because it is damaged or the customer decides to return it (e.g. it costs too much and he didn't realize it)
-
we have to manage the cancellation of a product, because it is damaged or the customer decides to return it (e.g., it costs too much and he didn't realize it)
-
the government stopped producing 1 and 2 cents coins:
- every bill/invoice has to be rounded to the nearest lower multiple of 5, even if paid with debit/credit card
...[to be continued]...
PS: feel free to propose next change request to implement! 😀