Why XCTest is not used for unit-tests?

[valeriyvan]

Just curious, why XCTest is not used for unit-tests?

[tayloraswift]

great question!

the corelibs (especially Foundation) have well-known issues with portability and binary size, so i try to minimize usage of them as much as possible. this matters more for the library targets than the test targets, but these days i have so much Foundation-less infrastructure built already, it makes a lot of sense to me to use it for the tests as well.

the downside as you’ve discovered is this does not work well with @testable, but my project-specific take on this is that PNGTests shouldn’t be using @testable at all; the currently non-public LZ77 APIs it is calling into should really be made public and split off into a separate LZ77 compression target that other libraries (like a future swift-gzip package) could depend on. (this is tracked by #22 .) so my vision is eventually PNGTests should become LZ77Tests with the non DEFLATE-related tests moving into PNGIntegrationTests, which should just become the new PNGTests.

the tests for this library are quite old so you might still see the occasional import Foundation.exit, but once i get around to fully migrating the tests to Testing those should be gone as well.