Do Your Quality Gates See The Brown M&Ms In The Bowl?

I see more and more converts to mutation testing, as folks learn that extending the horizon of agentic coding requires much, much stronger quality gates. Mutation testing deliberately injects errors into code to create “mutant” versions – like turning a + into a -, or replacing a string with “” – so we can see if any of our automated tests catch the error. If no tests fail and the mutant survives, that reveals a potential gap in the test suite. Mutation testing is a specialised version of what I’ve been calling “Brown M&M tests”. Perhaps you know the story – Van Halen had a clause buried in their venue rider that there should be a big bowl of M&Ms in the dressing room with all the brown ones taken out. Not an example of diva-like rock start excess, but a very practical test of whether the venue had paid attention to every detail. Van Halen’s live show had many complex technical elements. If they entered their dressing room and saw brown M&Ms in the bowl, they double-checked…