TDD Exam Questions

Last year I ran a three day in-house training on unit-testing and TDD using Eclipse. I wanted the course to be as interactive as possible to keep the attendees engaged all the time. Besides my slides I carried out exercises like Jason Gorman's TDD from Hell and played short movies to keep the content varied. At the end of each chapter I showed a slide with a few questions about the topic just covered. These questions gave the audience a break to recall the content just studied and reflect on it before moving on. I searched for such questions but did not find any, so I had to come up with my own.

These are my sanity-check questions. They are not complicated or long-winded, just simple questions to verify if the content was understood. Some questions also served as a base for further discussion. The developers in the audience were exposed to TDD for the very first time, so I kept them simple. If you are a seasoned developer I am sure these questions will not challenge you at all.

Unit Testing with JUnit

• What is a test fixture?
• Which assert is used to compare the values of objects?
• What about assertTrue(true);?
• What about assertTrue(a.equals(b));?
• How to test for an expected exception?
• What about System.out.println(...); in tests?
• How to data-drive tests?
• How to time-out tests?
• How to test the contents of a private field? (This is a trap, the answer is not to test it but to change the design.)
• Does full code coverage mean the code is fully tested?

Test Driven Development

• What are the benefits of using TDD?
• Is TDD primarily a testing technique?
• When do you write tests? (This is a joke and the expected answer is "all the f*cking time" according to Bryan Liles' TATFT.)
• What should you do when you cannot add another test?
• If the code passes all the unit tests why should you still change (refactor) it?
• Why not refactor on a red bar?

Mocking and Test Doubles

• Why use stubs or mocks?
• How are objects called that are passed around but never actually used?
• How are objects called that can return fixed values in answer to calls made.
• How are objects called that can verify the behaviour of the system under test, in addition to using asserts to verify its state.
• What is used for testing state?
• What is used for testing behaviour?
• What is a spy?

Refactoring

• What is your favourite Refactoring?
• How do we refactor? (This is a word play and the expected answer is mercilessly.)
• Should Refactoring and adding new code be done at the same time?
• During Refactoring, how long does your code not compile?
• During Refactoring, when should we run the tests?
• What Refactoring can be used when a method is too long, has duplicated code or Feature Envy?
• What Refactoring can be applied to long parameter lists?
• In Eclipse, what do the short-cuts Alt-Shift-R, Alt-Shift-L and Alt-Shift-M do?

Working with Legacy Code

• What is Legacy Code?
• How can you break dependencies?
• What are Singletons and why are they evil?
• Do you write them?

Using these questions, small exercises and short movies I kept the participants fully engaged for a whole day of TDD theory. It was awesome!