Mutation testing workshop

Setup

curl https://raw.githubusercontent.com/boxed/mutation-testing-workshop/master/start.sh | bash
cd scientist
source venv/bin/activate

Run tests

python -m hammett

Run coverage report

python -m pytest --cov scientist

Run mutation testing

mutmut run

Now write tests in tests/test_scientist.py and rerun mutmut until you have no surviving mutants!

Commands:

• mutmut show: see the list of mutants
• mutmut show 4: show mutant 4
• mutmut show all: see all the mutant diffs
• mutmut apply 4: apply the mutant 4 to disk
• python -m pytest: run tests

Tips:

• It can be useful to look at a few mutants at a time, especially if they are on the same line
• Mutation testing can be played in two ways:
  • Look at the diff, write a test that passes, do mutmut run to see if you wrote the test properly
  • Apply the mutant on disk, write a test that fails, revert the mutant, check that the test succeeds. You want to do mutmut run after too.