MEPX
Chapter 6 of 10All chapters
  1. 1Reading is the job
  2. 2Getting oriented
  3. 3Understanding a function
  4. 4Following state
  5. 5Recognising shapes
  6. 6Reading for trouble
  7. 7Using history
  8. 8Tests as documentation
  9. 9Taking notes
  10. 10Reading in review

Chapter 6 of 10

Reading for trouble

Where bugs like to hide.

The usual places

Boundaries: the first and last item, empty input, zero, null, and the moment a limit is reached. Most bugs live at an edge rather than in the middle of a happy path.

  • Off-by-one errors cluster around <= against < in loop conditions.
  • Error paths are the least tested code in almost every codebase.

Concurrency

Anything touching shared state from two places at once deserves suspicion. Timing bugs read perfectly well on the page, which is what makes them expensive.