Structure and Interpretation of Test Cases • Kevlin Henney • GOTO 2022 – YouTube (hello Leap Years!)
Posted by jpluimers on 2025/12/30
Any session by Kevlin is great, so this is definitely recommended watching: [Wayback/Archive] Structure and Interpretation of Test Cases • Kevlin Henney • GOTO 2022 – YouTube
Via [Wayback/Archive] Ifeora Okechukwu on Twitter: “On the structure and interpretation of test cases: by @KevlinHenney Awesome talk!!! “.
A few takeaways:
- Kevlin uses the same Leap Year case as I have taught since the mid 1990’s: I like the way we both approach software development, though I can still learn a lot from Kevlin.
- Non-programmers understand more than you might expect, just like you can get much more from a foreign news paper than you would think at first thought
- You should know how to draw a Venn diagram with 4 sets allowing *all* combinations of those (search for “Venn’s four-set diagram using ellipses” in the link on the left)
- Kevlin shows these 4 sets:
- Common cases
- Simple cases
- Boundary cases
- Edge cases
The first two and last two sound similar. They aren’t.
- Wrinkles and various levels of code coverage: don’t fool yourself as that is easy to do
- The way of thinking is “thorough” (note from self: AI is not thorough, it is statistics)
- Calendars are difficult (and depending a lot on the period and region their usage are valid for) – I already knew that, but it was good to be reminded off; see presentations by Jon Skeet for more information on it, see the blog tag Jon Skeet, or for instance these links:
- [Wayback/Archive] Jon Skeet’s coding blog
- [Wayback/Archive] Dates and times aren’t that hard – honestly! – Jon Skeet – YouTube
- [Wayback/Archive] More fun with DateTime | Jon Skeet’s coding blog
- [Wayback/Archive] Noda Time blog
- [Wayback/Archive] Understanding Dates, Times, and Time Zones, with Maggie Pint, Matt Johnson, and Jon Skeet | Microsoft Learn
- [Wayback/Archive] Common mistakes in date/time formatting and parsing | Jon Skeet’s coding blog
- [Wayback/Archive] Jon Skeet — Dates and times: Hard, but not impossible – YouTube
Oh, Kevlin also covers FizzBuzz mentioning the enterprise edition which I already covered quite some time ago because Isotopp brought it to my attention: FizzBuzz as interview question – video by Tom Scott.
The reason Kevlin covered FizzBuzz is to again emphasise there is always a wrinkle, which you can see with his coverage hierarchy:
- function coverage
- statement coverage
- branch coverage
- path coverage
- branch coverage
- statement coverage
Even with all of these at 100%, you still can make your tests clearer: they are a fundamental part of your code base.
Query: [Wayback/Archive] jon skeet date time at DuckDuckGo
--jeroen
The Wiert Corner - irregular stream of stuff 
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