Add mutation testing

[gvladika]

PR adds integration with Certora's Gambit mutation testing framework. Gambit receives Solidity file or list of files as input, and it will generate "mutants" as output. Those are copies of original file, but each with an atomic modification of original file, ie. flipped operator, mutated 'if' condition etc. Idea is to then run the test suite against the mutant. If all tests still pass, mutant survived, that's bad - either there's faulty test or there is missing coverage. If some test(s) fail, mutant's been killed, that's good.

gambitTester script works like this:

• generates mutants for files specified in test-mutation/config.json
• for each mutant do in parallel (in batches):
  • replace original file with mutant
  • re-compile and run foundry suite
  • track results
• report results

How to use it:

• update test-mutation/config.json with the list of solidity files to be tested
• run yarn run test:mutation

[yahgwai]

Nice! I'm looking forward to trying this out on our other projects. Is there a way to ignore a certain mutation if we know it's not useful information?

It might be nice to add a section the readme about how to do the mutation testing, including where to install gambit

[gvladika]

Nice! I'm looking forward to trying this out on our other projects. Is there a way to ignore a certain mutation if we know it's not useful information?

It might be nice to add a section the readme about how to do the mutation testing, including where to install gambit

I've added new doc with all the steps: d3e5df6

In the JSON config file (which is the input to Gambit for generating mutants), you can specify which kind of "mutation operators" you want to applied. Here is the list of all supported operators. You can also ie. limit mutation operators to the specific functions that you're interested in testing. Once mutated files are generated, currently there is no way to tell the testing script to skip some of them. But we can add that feature if it would be useful.

[gzeoneth]

LGTM