Your mission is to create a simple banking system. Think about your personal bank account experience. When in doubt, go for the simplest solution. Focus on building the domain logic, don't bother with creating any kind of user interface until it is explicitly requested.
The exercise evolves as a sequence of iterations. Try to complete each iteration before reading the next one.
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
Currently, users can deposit negative amounts of money, which does not make sense. Add a new test case to fix this issue.
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
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.
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.
- Are you keeping up with the requirements? Has any iteration been a big challenge?
- Do you feel good about your design? Is it scalable and easily adapted to new requirements that come up in further iterations?
- Is everything tested? Are you confident in your tests?
Expose the existing features (withdrawal and deposit) through a very simple Mobile app. No elaborate UI design or animations are needed at all.
Use the code written so far as a library. Put it in its own module/framework and add it as a dependency to the mobile application. You may tweak the existing code before beginning this iteration, but try not to change it in this iteration after you begin.
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.
Additionally, make this feature available through the Mobile app.