MEPX
Chapter 8 of 10All chapters
  1. 1Why test
  2. 2Kinds of test
  3. 3What a good test looks like
  4. 4Fakes, stubs and mocks
  5. 5Coverage and flakiness
  6. 6Reproducing a bug
  7. 7Narrowing it down
  8. 8Reading the evidence
  9. 9Debuggers and tools
  10. 10The hard ones

Chapter 8 of 10

Reading the evidence

Stack traces, logs and assumptions.

Start at the top

A stack trace names the file, the line and the path that got there. Read it before theorising: most of the time it says exactly what is wrong.

  • Check your assumption about what a value actually is at that moment.
  • The bug is usually in your code, not the library. Usually.

Logging deliberately

Log the values that would confirm or refute your hypothesis, not everything. Structured logs with a request id let you follow one journey through a busy system.