Issue Description:

Create a Package.swift like this

// swift-tools-version:5.2
import PackageDescription

let package = Package(
    name: "happn-swift",
    targets: [
        .target(name: "happn-swift", dependencies: []),
        .testTarget(name: "happn-swiftTests", dependencies: ["happn-swift"])
    ]
)

with the proper architecture around it.

Run swift test --enable-test-discovery on Linux.

Expected result: The test in the happn-swiftTests are run.

Actual result: We get the following compilation error

/tmp/.build/x86_64-unknown-linux-gnu/debug/happn-swiftPackageTestsTestlist.derived/main.swift:4:10: error: use of unresolved identifier '__allTests_happn_swiftTests'
tests += __allTests_happn_swiftTests()

Renaming the test target to happnSwiftTests (and updating the related folder name) does fix the test discovery.