bank-account-actions v1.1.1

Raul Perez

Confidential. Please do not make public this document or your solution.

VeriTran's 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. 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.

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.

Retrospective

• 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?

Iteration 6: Add a CLI

Expose the existing features (withdrawal and deposit) through a very simple CLI. No elaborate menus or interaction are needed at all.

Use the code written so far as a library. Put it in its own module/component and add it as a dependency to the CLI application. You may tweak the existing code before beginning this iteration, but try not to change it in this iteration after you begin.

Iteration 7: 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.

Additionally, make this feature available through the CLI.

New User Story:

Feature: Transfer money from an user account to another one
    As a client of the bank
    I want to transfer money from my account to another account
    In order to decrease my balance and increase the another account balance

    Scenario: An existing client transfer money to another client account
        Given an existing client with id “francisco” with 100 USD in his account and "lucas" with 20 USD in his account
        When "francisco" transfer 10 USD into "lucas" account
        Then the balance of "francisco" account is 90 USD and "lucas" balance is 30 USD