Testing large, untested code bases

Dr. C. Titus Brown


  • figlead

The code base

  • 8k of python, 2k of pyrex
  • Little app/UI code almost all library and framework
  • Grew of accretion and personal use at UCLA
  • Lots of technical debt

Issues with code base

  • written at high level throughout
  • lots of unfamiliar code
  • functional
  • Mix of developers
  • Crosses domains
  • Performance is critical

What we already know

  • Unit tests and functional tests rock: use ‘em
  • Code coverage is of limited utility because it doesn’t measure branch coverage
  • Code coverage is invaluable when aimed at:
    • new test efforts on legacy code
    • understanding code bases
    • legacy code is code that does not have systematic tests

Software forensics

  • understanding big code bases is hard
  • Code coverage can be used as a lever:
    • “Give me but a place to stand and with a lever I will move the entire world”

Grokking code thru coverage

  1. Start with minimum useful statement
  2. Examine code that’s actually executed
  3. Add additional statement
  4. Examine executed code
  5. Repeat