add test target to SPM

Author: miguelangel-dev

project/Package.swift

@@ -25,6 +25,7 @@ let package = Package(
         .target(name: "NefCarbon", dependencies: ["NefModels", "NefCore"], path: "Component/NefCarbon", publicHeadersPath: "Support Files"),
         .target(name: "NefSwiftPlayground", dependencies: ["Bow", "BowEffects", "BowOptics", "NefModels", "NefCommon"], path: "Component/NefSwiftPlayground", publicHeadersPath: "Support Files"),
 
+        .testTarget(name: "CoreTests", dependencies: ["NefCore"], path: "Tests/CoreTests"),
 
         .target(name: "nef", dependencies: ["Bow", "BowEffects", "Swiftline",
                                             "NefCommon",