tests/README

   1 * Test Anti-Patterns
   2
   3 OK, there are a few patterns that have been found over and over in the
   4 testing code base which makes the tests flaky. Here is an incomplete
   5 list. Don't do that.
   6
   7 1) Using pidof to wait for a background application (by name) to
   8    disappear.
   9
  10    Why is it flaky ?
  11
  12    The application may be delayed after being forked, but not executed
  13    yet. Therefore, pidof will not find it. Use "wait" instead.
  14
  15 2) Using sleep as delay-based optimistic synchronization technique.
  16
  17    Why is it flaky ?
  18
  19    Everything that needs to happen before/after other things need to
  20    be explicitly synchronized using e.g. a file (used as a flag).
  21    Sleep is just an indicator of a minimum arbitrary delay, but
  22    machine load and scheduling can actually mess up the real delay
  23    between applications. Use explicit synchronization points. Never
  24    sleep.
  25
  26 3) Using killall on a background application.
  27
  28    Why is it flaky ?
  29
  30    Similarly to pidof, killall may run before the background application
  31    executes, thus failing to find it. Store the application PID after it
  32    it launched in background into a temporary variable for later use
  33    by kill and wait.
  34
  35 4) Using wait ${!} to wait for completion of many background
  36    applications.
  37
  38    Why is it flaky ?
  39
  40    It just waits for the last application put in background. Use
  41    "wait" to wait for all background applications.
  42
  43 5) Forgetting wait at the end (or error return path) of a test phase
  44    that has background applications.
  45
  46    Why is it flaky ?
  47
  48    Those application may interact with the following testing phases,
  49    thus skewing the results.
  50
  51 6) Not grepping into the entire code base for similar patterns.
  52
  53    When you find a problematic coding pattern, chances are it appears
  54    elsewhere in the testing code base. Please fix it everywhere!
  55
  56 7) Introducing a utility abstraction without changing all open coded
  57    similar code path.
  58
  59    When an abstraction for e.g. starting and stopping the session daemon
  60    is introduced as a utility (e.g. utils.sh), future changes will
  61    assume that all the testing code base is using this abstraction.
  62    Leaving a few custom open-coded sites of duplicated code around is a
  63    good way to make it a pain to update the abstraction in the future.