It's hard to come up with good teaching examples of TestDrivenDevelopment that are large enough to be meaningful but small enough to be understood quickly. There are some old chestnuts: Kent Beck used the Money example in Test Driven Development: By Example (0321146530). Uncle Bob Martin and Ron Jeffries have frequently used the Bowling Game example.
Step by step examples
Ron Jeffries' Adventures in C#: The Bowling Game explores bowling scoring in C#.
William Wake's Test-First Challenge builds a spreadsheet program in Java. This is one of the best on-line demos I know, as it lets you write the code to make his tests pass. Translating the tests to other languages should be simple. There are also links to several solutions.
William Wake's The Test-First Stoplight includes a simple Java example of a Person class.
Will Stott and James Newkirk's Test-Driven C#: Improve the Design and Flexibility of Your Project with Extreme Programming Techniques includes some simple examples
Christopher Bennage's TDD Example: Querying a Repository shows a simple test using a database and C#.
Brian Marick's A workbook for practicing test-driven design (draft) uses Java to develop an interface for a simple hierarchical data format.
Scott Bellware's Test-Driven Development Example: Factorial walks through developing a factorial calculator in C#.
Olof Bjarnason has collected his own list of TDD Problems
Code that's been developed using TDD
Brian Button's example of TDDed code
Problem suggestions that might make good examples
- A mailing list that supports entering a future address change for a person
Alistair Cockburn's Coffee Machine might make a good example problem. (also see part 2.)
Descriptions and explanations of TDD
Scott Ambler's Introduction to Test Driven Design has a good description before it dives into Test Driven Database Development.
Nancy Corbett's Test Driven Development, a Portable Methodology at Developer.com