[twic]

This sounds a lot like a couple of old JUnit test runners:

InfiniTest - https://infinitest.github.io/ an dhttps://infinitest.github.io/doc/intellij#how-it-works

JUnit Max - https://web.archive.org/web/20090206151635/http://www.threer... partially surviving as https://junit.org/junit4/javadoc/4.12/org/junit/experimental...

Ruby has something similar:

autotest - https://github.com/grosser/autotest

I think it's a good idea, and i'm surprised it hasn't become a standard feature of IDEs and test runners.

[Cthulhu_]

Jest, probably the most popular JS test runner of today, also has had it since forever.

[solardev]

My Jest can run on only changed files, but it still takes forever. Much longer than 250ms

[_cfl0]

Right.. Because out of a 100 tests it will run close to that number. when you change code most of the time only a handful of tests or less need to run.

[_cfl0]

Had what since forever? Does jest analyze the changes you make and compare them to code coverage? (hint: no)

The key innovation piece here is the speed that the extreme selectively enables you.

[grncdr]

Ruby also has crystalball (https://toptal.github.io/crystalball/) which is similar, but not quite the same.

[_cfl0]

Main difference is that crystalball still runs all the tests, but runs the recently failed ones first.

Nabaz selects a small subset of affected tests, reducing CPU usage, and more importantly improving speed drastically!