[CamouflagedKiwi]

Well no, it's just not build agent size; if you have 10 tests that take 3-4 minutes each, you're not gonna go any faster than the slowest of them (plus the time to build them, which is also typically bad for those kinds of tests, although a bigger build agent may be faster there). Having a system that can avoid running the test for many PRs because it can prove it's not affected means in those cases you don't have to wait for that thing to run at all.

Although, time is money, so often scaling build agents may be cheaper than paying for the engineering time to redo your build system...

[bluGill]

I have hundreds of tests that take 15-30 mintues each. These tests tend to be whole system tests so there is no way useful way to say it won't touch your change (75% will). Despite an extensive unit test suite (that runs first) these tests catch a large number of real production bugs, and most of them are things that a quicker running test couldn't catch.

Which is to say that trying to avoid running tests isn't the right answer. Make them as fast as you can, but be prepared to pay the price - either a lot of parrell build systems, or lower quality.