I think we should fail if invalid subshard name, I spent some time debugging why my shard was running integration tests and turns out that if you make this mistake _selectIndexOfTotalSubshard returns an empty array which then on _runDartTest if you pass an empty array you end up with a command like this run test --flags and then it runs every single test on your workingDirectory. I will make an issue to fix this

Originally posted by @Jasguerrero in #112505 (comment)