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As this is our first XCTest extension it's a bit tricky to work out where everything goes, so this is mainly starting as a discussion.

Checklist

• I checked the Contributing Guidelines before creating this request.
• New extensions are written in Swift 5.0.
• New extensions support iOS 10.0+ / tvOS 9.0+ / macOS 10.10+ / watchOS 2.0+, or use @available if not.
• I have added tests for new extensions, and they passed.
• All extensions have a clear comments explaining their functionality, all parameters and return type in English.
• All extensions are declared as public.
• I have added a changelog entry describing my changes.

Issues

Targets

Source files that include XCTest can only be added to test targets.
This means that they can't be included in the frameworks in the Xcode project, which means that they can't be included in Carthage.
If a non-test target makes any reference to XCTest, even if it's protected by

#if canImport(XCTest)
import XCTest

it will throw a build-time error saying Failed to load module 'XCTest', so it will probably cause projects to fail building if we add it via CocoaPods and, probably, SPM.

Location

Where do the source files belong? If we place them in Sources/SwifterSwift/XCTest then they will be included in the Swift package, unless we add that folder to the excludes list, which is easy enough.
However, if we add it to Tests/XCTest then people may miss those extensions because they never open that folder. Maybe not 🤷‍♂️

Imports

In order to use Color in this example I need to call @testable import SwifterSwift, which may cause problems if we do find a way to make these extensions part of the framework. A solution would be to copy the typealiases.
Regardless, it's not really an issue unless we can actually include it in the library along with the other files anyway.

New project

An alternative is to actually have a separate project, let's say called SwifterTests, which has SwifterSwift as a dependency. It would allow anyone who's mad enough to include the entire project as a dependency to include SwifterSwift for their project and SwifterTests to their test targets. E.g.

target 'MyApp' do
   pod 'SwifterSwift'

   target 'MyAppTests' do
      pod 'SwifterTests'
   end
end

Obviously there are a bunch of issues here, the main one being visibility, but I think it's the cleanest option.