Swift Testing Implementation

[ethan-vanheerden]

This PR introduces a Swift Testing-based solution for TestableCombinePublishers.

1. It creates a new SwiftTestingTestableCombinePublishers target which mimics the existingTestableCombinePublishers target, but with no usage of the XCTest library.
   • This new target was created so that clients explicitly need to opt into the Swift Testing version - as XCTest and Swift Testing can have undefined behavior when they are used in the same test suite.
2. I also created a new TestableCombinePublishersUtility target which houses shared logic between the XCTest and Swift Testing implementations - i.e. AutomaticallyEquatable

The only different between the XCTest and Swift Testing implementation is that the Swift Testing implementation utilizes async/await:

TestableCombinePublishers

SwiftTestingTestableCombinePublishers

func testExpectEquatableValue() {
        ["cool"]
            .publisher
            .expect("cool")
            .waitForExpectations(timeout: 1)
}

@Test func expectEquatableValue() async {
        await ["cool"]
            .publisher
            .expect("cool")
            .waitForExpectations(timeout: 1)
}

[albertbori]

Hey Ethan! Thanks a ton for taking a stab at this. It looks really good. I left a handful of comments for tidying things up. Can't wait to get this merged!

Edit: I'm also curious if there's opportunity here to reshape the expectation API by utilizing Combine Publisher's value parameter, which returns an async sequence of elements from the publisher. The reason I didn't do this originally is because I didn't have a timeout mechanism. Now that we do, assuming that ["cool"].publisher.value supports cooperative cancellation, we may be able to reshape the expectation code.

Regardless, I think we can explore that later as part of a new major version. You're on the right track here with this PR.

[albertbori]

Looks great! Fantastic work!