Bank - Ruby

This is a small project to practice maintaining code quality and process. Source

I have created a JavaScript implementation for the browser, and in node. I have also made a Python implementation, available here.

It allows you to create an account, deposit funds into it, withdraw funds from it, and print statements.

• Spec
  • Requirements
  • Acceptance criteria
• Quick Start
• Screen Preview
• Gems
  • Rubocop Configuration
• Development Journal
  • Domain Modelling
  • User Stories
  • Set up
  • Accounts
  • Deposits
  • Withdrawals
  • Statement
  • Transactions
  • Back to Account Statement
  • Simplecov and Rubocop
  • Pretty Deposit & Withdraw Returns
  • Pretty Print Statement
  • Extracting a Printer Class
  • Refactoring To Use Pence

Spec

Requirements

• You should be able to interact with your code via a REPL like IRB or the JavaScript console. (You don't need to implement a command line interface that takes input from STDIN.)
• Deposits, withdrawal.
• Account statement (date, amount, balance) printing.
• Data can be kept in memory (it doesn't need to be stored to a database or anything).

Acceptance criteria

Given a client makes a deposit of 1000 on 10-01-2012
And a deposit of 2000 on 13-01-2012
And a withdrawal of 500 on 14-01-2012
When she prints her bank statement
Then she would see:

date || credit || debit || balance
14/01/2012 || || 500.00 || 2500.00
13/01/2012 || 2000.00 || || 3000.00
10/01/2012 || 1000.00 || || 1000.00

Quick Start

1. Clone this repo.

2. Install dependencies with:

   bundle

3. Run test suites with:

   rspec && rubocop

4. Launch IRB:

   irb

   Once in IRB.

   require './lib/account.rb'
   account = Account.new
   

5. Use your account with the following methods

Method	Description
account.deposit(number)	deposit however much you want into your account, this figure is in pounds with pence as decimals.
account.withdraw(number)	withdraw however much you want from your account, this figure is in pounds with pence as decimals.
account.statement	prints a statement of all transactions so far

You should see something similar to the below in your terminal:

Screen Preview

Gems

This project has no production dependencies.

Testing and Development gems are:

Gem	Description
rspec	Testing framework
rubocop	Linter, checks for code quality and conventions
simplecov	Measures test coverage
simplecov-console	Displays measured test coverage when rspec is run

Rubocop Configuration

Rubocop config is specified in .rubocop.yml.

Configured to ignore any file in the spec directory, and the Gemfile.

I have also disabled to documentation ruleset, to prevent it applying the Missing top-level class documentation comment rule (which for this small project is a bit overkill).

Development Journal

Domain Modelling

CRC modelling:

User Stories

• 1

As a Bank Manager,
So that we only take customers money,
I want accounts to start with balance 0

• 2

As a Customer,
So I can keep my money safe,
I want to be able to deposit into my account

• 3

As a Customer,
So I can spend my money,
I want to be able to withdraw from my account

• 3.1

As a Bank Manager,
So we don't go out of pocket,
I want withdrawals to only be allowed to occur if the customer has sufficient funds

• 4

As a Customer,
So I can keep on top of my finances,
I want to be able to print my account statement

• 4.1

As a Customer,
So I know when each transaction happened,
I want transactions on my statement to have the date

• 4.2

As a Customer,
So I know how much each deposit was,
I want deposits on my statement to have the credit amount.

• 4.3

As a Customer,
So I know how much each withdrawal was,
I want withdrawals on my statement to have the debit amount.

• 4.4

As a Customer,
So can keep track of my balance,
I want transactions on my statement to have the balance amount after the transaction was completed.

• 4.5

As a Customer,
Because more recent transactions are more important to me,
I want the statement transactions to be ordered from newest to oldest.

Set up

Initialised with Bundler, and added RSpec to the Gemfile in test/dev groups, then bundled to install.

Initialised RSpec.

Accounts

• 1

As a Bank Manager,
So that we only take customers money,
I want accounts to start with balance 0

In spec/account_spec.rb wrote a test for an Account class that is initialised with a balance of 0. Red.

In lib/account.rb:

• Added class Account with initialize method setting balance attribute with 0, exposed as readable.

Deposits

• 2

As a Customer,
So I can keep my money safe,
I want to be able to deposit into my account

Test for Account for a deposit method taking 100 results in a balance of 100. Red.

• Added deposit method with amount as param, sets balance to 100 hardcoded.

Green.

Test for Account for a deposit method taking 200 results in a balance of 200. Red.

• deposit method sets balance to the amount passed.

Green.

Test for Account for two deposits, one of 100 and another of 300, results in balance of 400.

• deposit method uses += instead of just assigning @balance with amount

Withdrawals

• 3

As a Customer,
So I can spend my money,
I want to be able to withdraw from my account

Test for Account for a withdraw method. In the describe block added a before block to deposit 1000, so there is something to withdraw.

Test for withdraw 100 results in a balance of 900. Red.

• Added withdraw method taking amount as param, sets @balance to 900 hardcoded.

Test for withdraw 200 results in balance of 800. Red.

• withdraw now sets @balance as @balance less the withdrawn amount with the -= operator.

Green.

• 3.1

As a Bank Manager,
So we don't go out of pocket,
I want withdrawals to only be allowed to occur if the customer has sufficient funds

Test for withdraw 1500 results in error: Insufficient funds.

• within withdraw, if @balance is less than amount raise 'Insufficient funds'

Green.

Refactored to guard clause from if block.

Later refactored to simply return a string 'Insufficient funds', rather than raising a runtime error.

Statement

• 4

As a Customer,
So I can keep on top of my finances,
I want to be able to print my account statement

In spec/account_feature_spec.rb wrote a feature test based on the above acceptance criteria. Red.

• Added statement method to account.
• Hardcoded the response based on the expected statement.

Green.

Wrote another feature test with different figures. Red.

For this I think I should implement the Transaction class.

Transactions

• 4.1

As a Customer,
So I know when each transaction happened,
I want transactions on my statement to have the date

In spec/transaction_spec.rb added a test for Transaction class, it's display method returns a string in the format of a transaction row on a statement, with the time in the first column. Red.

In lib/transaction.rb:

• Transaction class initialised with time as Time.now.
• formatTime private helper method formats the time as the required "dd/mm/yyyy" string.
• display method returns the formatTime result into a string with columns as per the statement transaction row.

Green.

• 4.2

As a Customer,
So I know how much each deposit was,
I want deposits on my statement to have the credit amount.

Test for display method to return a string in the format of a transaction row on a statement, with the time in the first column, and credit in second column when initialised with a credit keyword argument.

• Transaction initialise takes a keyword argument credit defaulting to nil, used to set @credit.
• private helper method creditFormat checks if @credit is truthy then returns it as string with trailing space (easiest way I could find to get correct formatting).
• Display interpolates the creditFormat in the second column.

Green.

• 4.3

As a Customer,
So I know how much each withdrawal was,
I want withdrawals on my statement to have the debit amount.

Test for display method to return a string in the format of a transaction row on a statement, with the time in the first column, and debit in third column when initialised with a debit keyword argument.

• Transaction initialise takes another keyword argument debit defaulting to nil, used to set @debit.
• private helper method debitFormat checks if @debit is truthy then returns it as string with trailing space.
• Display interpolates the debitFormat in the third column.

Green.

• 4.4

As a Customer,
So can keep track of my balance,
I want transactions on my statement to have the balance amount after the transaction was completed.

Test for display method to return a string in the format of a transaction row on a statement, with the time in the first column, and balance in third column when initialised with a balance keyword argument.

• Transaction initialise takes another keyword argument balance defaulting to nil, used to set @balance.
• display method interpolates balance in last column (no need for formatting helper here as it is the last column).

Refactored the very similar creditFormat and debitFormat methods into a general method format that can accept either as an argument. The format method also uses a guard clause rather than an if block for brevity.

Wrote a test that makes use of all keyword arguments to make sure the display method works as intended.

It was also at this point i noticed that the figures should be displayed with trailing ".00", so adjusted the tests for that.

• Added a .00 after the formatted item in the format method.
• Also passed @balance through this in the interpolated display.

All tests Green.

Back to Account Statement

• 4

As a Customer,
So I can keep on top of my finances,
I want to be able to print my account statement

Now the Transaction class is implemented, the Account deposit and withdraw methods can create transactions that the account can hold. The Account statement method can loop through the held transactions, using their display methods to add to the statement.

Wrote a test that the Account should use the Transaction class, and deposit method should call for a new transaction with the amount as credit and the new balance as balance. This test mocks the Transaction class and expects it to receive .new.

• Injected the Transaction class to allow for testing in isolation.
• deposit method creates a new instance of transaction with the credit amount and resulting balance.

Green.

Wrote a test that the withdraw method should call for a new transaction with the amount as debit and the new balance as balance. This test mocks the Transaction class and expects it to receive .new.

• withdraw method creates a new instance of transaction with the debit amount and resulting balance.

Green.

In order to satisfy the feature test with the statement:

• Added a @transactionHistory initialised as an empty array.
• In the deposit and withdraw methods the new transaction instance is unshifted onto the @transactionHistory array (so they go at the front of the array).
• The statement method has a header variable which is the column titles ending with a newline.
• a variable, statementRows is created by mapping through the @transactionHistory array, and calling each transaction's display method.
• statement returns the header concatenated with the statementRows joined with newline characters.

Green.

Refactors:

• Extracted private helper methods addDepositTransaction and addWithdrawTransaction from deposit and withdraw taking the same keyword arguments as the new method call they used before.
• Extracted constant STATEMENT_HEADER from the statement method.
• Used &:display in the statement map to proc the display method on the element rather than using a full map block.

Simplecov and Rubocop

Added simplecov and simplecov console gems and configured them in spec_helper.rb to check code coverage (better late than never). Also added coverage to .gitignore.

Linting all files with Rubocop led to minor formatting fixed (also added Rubocop to gems so anyone can run these tests).

Based on Rubocop suggestions:

• Renamed several variable and method names to snake_case convention (been doing too much JavaSript it seems).
• Excluded spec files in .rubocop.yml as these tend to have large blocks and long lines (e.g. the result of the feature tests.)

Also:

• Account initialise method sets @balance with new constant STARTING_BALANCE as 0.

Pretty Deposit & Withdraw Returns

I realised I was testing state of @balance rather than behaviour.

Reworked tests to check for a returned string with the amount deposited/withdrawn and the resulting balance. Red.

• Added to deposit and withdraw a string interpolating the amount deposited or withdrawn and new balance.
• Removed attr_reader for @balance as it is no longer needed.

Green.

Pretty Print Statement

Adjusted the feature tests to check for output to standard out rather than just for the returned value. Red.

Added a puts to the statement so the result is printed out properly, rather than returning a poorly formatted string.

Green.

Extracting a Printer Class

It was pointed out to me that there could be a printer class.

In spec/printer_spec.rb:

Wrote test for a print method, passing "Hello World" prints "Hello World" to stdout with a newline. Red.

In lib/printer.rb:

• Added a Printer class with method print that puts "Hello World"

Green.

Wrote test for the print method, passing "Hi There" prints "Hi There" to stdout with a newline. Red.

• print puts what you pass in as argument.

Green.

Wrote test for the print method, passing an array prints each element on a new line. Red.

• Added an if else statement to check if the item passed is a string, if so puts it, else it is an array to join with new lines and puts that

Refactored to use a ternary operator.

Wrote test that statement uses printer class.

• Injected the new Printer class into the Account class with keyword argument to initialize.
• @printer is assigned with a new instance of the injected printer.
• Reworked statement to print using @printer.print.

Refactoring To Use Pence

In lib/conversion.rb:

• Created a new module, Conversion.
• Created a new method, to_pence, taking an amount, multiplying by 100 then converting to integer.
• Created a new method, as_pounds, calling the sprintf method with two decimal places, and the passed amount (as pence) divided by 100.

Included this module in Account and Transaction classes.

• Inputs sanitised to pence with to_pence.
• Return strings etc format from pence to pounds with 2 decimals with as_pounds.

Refactored as_pounds to use the format method instead of sprintf as per Rubocop suggestion.