MEPX
Chapter 5 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 5 of 10

Coverage and flakiness

Two numbers that mislead.

Coverage

Coverage measures which lines ran during tests. It is useful for finding untested areas and worthless as a target, because a test with no assertions covers everything and proves nothing.

  • Chasing a percentage produces tests written to touch lines.
  • Look at what is uncovered rather than at the number.

Flaky tests

A test that fails intermittently is worse than no test, because it teaches everyone to rerun the build. Fix it or delete it; leaving it is a choice to ignore failures.