Author here. Mill also helps with running tests. Apart from all tests running parallel by default with heuristics to try and maximize performance (https://mill-build.org/blog/11-jvm-test-parallelism.html), Mill also can selectively execute tests in CI based on code changes (https://mill-build.org/mill/large/selective-execution.html), and provide performance profiles so you can see what is taking up time and improve it (https://mill-build.org/mill/depth/parallelism.html#_mill_chr...). All this is built in and comes for free, with the end result that even tests can take much less time in Mill than they do in other build tools

Thanks for jumping in, that’s actually really helpful context. Parallelism and selective test execution built-in sounds like a huge win, especially for CI and larger teams. I’ll admit the Scala dependency still makes me hesitate a bit for pure Java projects, but clearly Mill’s design is tackling real pain points head-on. Definitely tempted to try it out on a greenfield project.

True. Tests usually dominate the time budget. But from what I've experienced, slow builds still hurt, especially when you're iterating frequently or working across multiple modules. Those 10–20 seconds of wait adds up fast when you're in the zone and trying things out.