iOSDev UK: Using TDD to write an iOS App

Graham Lee, professional in-betweener, @iamleeg

Or, “What is TDD and why should you use it?”

• discovering bugs is not the point of testing at all
  • instead, you are proving that there aren’t bugs
• once we’ve fixed bugs, we don’t want to see them ever again
  • tests can ensure that regressions don’t come back
• TDD allows us to prevent bugs from ever happening!
  • you won’t prove that the app works how the customer expects, but you will at least prove that it works how you expect it to work…
• TDD imposes black-box thinking for the developer
  • makes you think about how the code should be designed and scoped
• accurate planning: we know how much we’ve done
  • and we can be honest how much we have done
• TDD does not:
  • ensure that the developer understood the requirements!
  • ensure that the requirements remain static
  • ensure that pieces work together (unless you add integration tests)
• tests should be short and have descriptive, English names
  • e.g. testDatesOnTheSameDayAreConsideredSame
  • general pattern
• tests should be fast — well under a hundredth of a second each, so a second or so for all of them
  • avoid integration tests in unit testing since they take too long
  • don’t interrupt your concentration by waiting for tests
• as a result, your classes will be smaller and have obvious effects
  • any side-effects are few and easy to predict
  • if your test fixture gets big, then that’s a sign that you need to refactor (possibly including the tests!)
• TDD encourages “tell, don’t ask” configuration
  • inversion of control
  • pass in helper data rather than discover it internally
• avoiding testing everything at once:
  • use fake objects (with same interfaces) to provide simulated interactions
  • use mock objects to record and verify interactions
• Objective-C mock frameworks:
  • OCMock
  • Mocky
• Code coverage is useful for adding tests to an existing app
  • Not so useful for building new code
  • If you’re not covering code with TDD, then you’re kind of cheating yourself

Q&A

• @pilky knows about using the accessibility framework to write automated UI tests using javascript
• can use XCodeBuild to run unit tests from command line
• use GHUnit instead of built-in OCUnit to output JUnit XML reports
• iOS Enterprise Development — O’Reilly book by James Turner
  • includes lots of useful
• squish automated GUI testing?
• test code linking…
  • app should be plugin host, providing linked libraries
  • but it doesn’t work — have to link yourself from test code