Track 17 · Lesson 9 of 12

Project: community library system with tests

Model a lending library with Book, Member and Library classes, enforce loan rules and late fees with clear errors, then write tests that prove the rules hold.

You will be able to

• Design a small domain model of cooperating classes from a requirements brief
• Enforce business rules with validation and a custom exception that carries a clear message
• Calculate due dates and late fees from dates passed in, so results are reproducible
• Write test functions that pin down the rules, including boundaries and error cases
• Judge the strength of a test suite by whether it catches deliberately broken versions of the code