I agree that parallelization is often a good way to speed up your CI pipeline, but the OP's suggestion of shifting integration tests to unit tests is frequently

I agree that parallelization is often a good way to speed up your CI pipeline, but the OP's suggestion of shifting integration tests to unit tests is frequently the worst thing you can do because it very often changes a test that tests into a test that is just a pale imitation of the code under test - a mimetic test. I worked on a big old ball of mud once where business logic was smeared across 6 or 7 different microservices. The ONLY way to gain confidence that the app did the right thing was to test it end to end which, of course, took ages, and meant hours long CI pipeline (longer if not parallelized). My coworker tried to replace some of those tests with "faster" unit tests around bits of those microservices but all they did was "lock down" the horrible architecture such that it became impossible to refactor and consolidate the business logic without breaking a bunch of unit tests.