Session 8

TDD Exploration for the Project, Take 2

810:188
Agile Software Development

Exploratory Programming on the Project

I posted my one-page story for the project, of the sort story you were asked to write based on Jason Fried's article. We discussed some of the project requirements we learned more about yesterday, when we implemented a simple story or two about the user recording transactions in the general journal.

Then we explored the system from the other end, where it produces summary reports. We paired up, took a simple story, wrote a test, and wrote code. The story:

The user requests a balance sheet as of today.

We assumed a small set of accounts, one or two assets and one or two liabilities. Some pairs moved on to a second story:

The user requests an income statement for the current period.

Again, by writing code to solve even one test, the team learned some new things about the system to be built. For example,

• These reports are about accounts, not transactions.
• Who knows whether an account is an asset or liability? The account objects may well need to in the future, but for these stories the code needs only receive a collection of assets and a collection of liabilities.
• Net worth will be a standing account in the ledger. It is part of the equilibrium of double-entry accounting, part of its security mechanism. That is different from net income as reported on the income statement, which exists as an account only ephemerally, as part of the year-end closing process.
• If we had a collection of accounts, we could use Ruby's iterators to process them. This is the first hint that we might later want a ledger object.
• Balance sheets and income statements share a common structure and even common arithmetic. The simplest thing that could possibly work right now might be a single, configurable method.

Some students also began to think about how they will end up representing money. Our exploratory code thus far has gotten by with strings, but as numbers... they are not floating point numbers!

Wrap Up

• Homework. None today.


• Reading. Version control is important, so I'd like you to read about another style of VCS, centralized version control. We will study Subversion (SVN).
  • The basic concepts of version control and SVN. (This is part of a complete on-line book about Subbversion.)
  • Source control in ten minutes, a shorter introduction to source code control and SVN, from Rice.
  • Subversion - A Quick Tutorial, another short tutorial for beginners, with examples of a local repository.
  • One more introduction, more like a cheat sheet, focused a bit on Windows, and perhaps aimed at a savvier reader.


• Programming. And keep practicing Ruby. Do NOT work on the accounting system code form today or yesterday. Try writing some stuff just for yourself.