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DDD Code Exercise

Background

Your mission is to create a simple banking system. Think about your personal bank account experience. When in doubt, go for the simplest solution. You don’t need to create any kind of user interface or make these features available through any server. The exercise evolves as a sequence of iterations. Try to complete each iteration before reading the next one.

What to do

Iteration 1: Add the deposit feature

You can follow this user story:

Feature: Deposit money into an account As a client of the bank I want to deposit money into my account In order to increase my balance

Scenario: An existing client deposits money into his account
    Given an existing client with id “francisco” with 100 USD in his account
    When he deposits 10 USD into his account
    Then the balance of his account is 110 USD

Iteration 2: Update the deposit feature

Currently, users can deposit negative amounts of money, which does not make sense. Add a new test case to fix this issue.

Iteration 3: Add the withdrawal feature

You can follow this user story:

Feature: Withdraw money from an account As a client of the bank I want to withdraw money from my account In order to have cash

Scenario: An existing client withdraws money from his account
    Given an existing client with id “francisco” with 100 USD in his account
    When he withdraws 10 USD from his account
    Then the new balance is 90 USD

Iteration 4: Cover border cases for the withdrawal feature

Add a scenario in the withdrawal feature for the case when a withdrawal generates an overdraft. Withdrawal of amounts bigger than the current account balance must not be allowed.

Iteration 5: Update the withdrawal feature

Check whether it is possible to withdraw a negative value. If it is possible, fix it. Add the corresponding test case to fix this issue.

Iteration 6: Add the transfer feature

From now on, users will be able to transfer money from their account to the account of another user. Add this feature. First write a user story for it. Write the scenarios for the main case, but also write scenarios for border cases, such as: can one transfer money one doesn't have? There may be others.

Scenario1: An existing client transfer money from his account to another client Given an existing client1 with id “francisco” with 100 USD in his account Given an existing client2 with id “pedro” with 50 USD in his account When the client1 transfers 10 USD from his account to the client2 Then the new balance the client1 is 90 USD and for the client2 is 60 USD

Iteration 7: Expose business logic through a rest controller

Steps for using the REST API

Start the aplication with mvn spring-boot:run
Examples
Create a new client francisco
	curl  -H "Content-Type: application/json" -X POST http://localhost:8080/client/francisco/100
	
Create a new client pedro
	curl  -H "Content-Type: application/json" -X POST http://localhost:8080/client/pedro/50
	
Deposit 10 to Francisco 
	curl  -H "Content-Type: application/json" -X POST http://localhost:8080/deposit/francisco/10
	
Withdraw 10 from Francisco 
	curl  -H "Content-Type: application/json" -X POST http://localhost:8080/withdraw/francisco/10
	
Transfer 10 from Francisco to Pedro
	curl  -H "Content-Type: application/json" -X POST http://localhost:8080/transfer/francisco/pedro/10

For the full API see http://localhost:8080/swagger-ui.html#/simple-banking-controller

Iteration 8: Add the account statement feature

Users have been using the system for a while now. But they are lacking a way to view all operations that have happened in their account. Add the account statement feature. Remember: it is not necessary to print to the console or send the statement data anywhere.

You can follow this user story:

Feature: Obtain the account statement As a client of the bank I want to obtain the statement of my account In order to review all operations that have occurred in it

Scenario: An existing client obtains the statement of his account Given an existing client with id “francisco” Given an existing client with id “pedro” Given francisco first deposited 100 USD in his account Given francisco then withdrew 20 USD from his account Given francisco then transferred 50 USD from his account to pedro's account Given francisco then deposited 10 USD in his account

When he obtains the statement of his account

Then the balance contains four lines, in the following order

  1. deposit, 100 USD, balance: 100 USD
  2. withdrawal, 20 USD, balance: 80 USD
  3. transfer to pedro, 50 USD, balance: 30 USD
  4. deposit, 10 USD, balance: 40 USD