delphiXtreme

For some time the (for lack of a better word) founder of BDD, Dan North, has been working on a BDD framework from Java called jBehave. The idea behind jBehave is to make stories and their associated scenarios executable. I’ve sent some time looking at jBehave and decided it looked a little too cumbersome for my taste. This week Dan released rBehave for the Ruby language. For some reason I’ve been able to sink my teeth into this more than jBehave. As such, I’ve started a Delphi implementation. Using Dans example story and scenarios:

Story: transfer to cash account
  As a savings account holder
  I want to transfer money from my savings account
  So that I can get cash easily from an ATM

  Scenario: savings account is in credit
    Given my savings account balance is $100
    And my cash account balance is $10
    When I transfer $20
    Then my savings account balance should be $80
    And my cash account balance should be $30

  Scenario: savings account is overdrawn
    Given my savings account balance is -$20
    And my cash account balance is $10
    When I transfer $20
    Then my savings account balance should be -$20
    And my cash account balance should be $10

(For more on BDD stories see Dan North’s article What’s in a Story)

I’ve come up with some code that looks like this:

procedure TransferToCashAccount.SavingsAccountIsInCredit;
begin
  Given('my savings account balance is', 100, SavingsAccountBalanceKey);
  Given('my cash account balance is', 10, CashAccountBalanceKey);
  When('I transfer', 20, DoTransfer);
  &Then('my savings account balance should be', 80, SavingsAccountBalanceKey);
  &Then('my cash account balance should be', 30, CashAccountBalanceKey);
end;

procedure TransferToCashAccount.SavingsAccountIsOverdrawn;
begin
  Given('my savings account balance is', -20, SavingsAccountBalanceKey);
  Given('my cash account balance is', 10, CashAccountBalanceKey);
  When('I transfer', 20, DoTransfer);
  &Then('my savings account balance should be', -20, SavingsAccountBalanceKey);
  &Then('my cash account balance should be', 10, CashAccountBalanceKey);
end;

The elements in play are:

• Given - sets a value in the world (context)
• When - executes an action
• Then - verifies that a value in the world (context) is that which is specified

There is one other element that’s not immediately visible here: the World. The world is simple a holding area for values. In this case we store the values of the savings account balance and the cash account balance in the world for manipulation in the When action. The DoTransfer method looks like this:

procedure TransferToCashAccount.DoTransfer(Value: Variant);
var
  TransferAmount,
  SavingsAccountBalance,
  CashAccountBalance : Currency;
  AccountTransferObject : IAccountTransfer;
begin
  TransferAmount := Value;
  SavingsAccountBalance := World[SavingsAccountBalanceKey].Value;
  CashAccountBalance := World[CashAccountBalanceKey].Value;
  AccountTransferObject := TAccountTransferObject.Create;
  AccountTransferObject.TransferAmount(SavingsAccountBalance, TransferAmount, CashAccountBalance);
  World[SavingsAccountBalanceKey].Value := SavingsAccountBalance;
  World[CashAccountBalanceKey].Value := CashAccountBalance;
end;

I built this on top of DUnit both for speed and the ability to mix these executable stories in with the unit tests or BDD specs used to implement the code. You can check out what I’ve done so far here:
dBehave.rar

What do you think?

BDD