// swift-tools-version:4.2

import PackageDescription

let package = Package(
    name: "ValidationToolkit",
    products: [
        .library(
            name: "ValidationToolkit",
            targets: ["ValidationToolkit"])
    ],
    targets: [
        .target(
            name: "ValidationToolkit",
            path:"Sources"),
        .testTarget(
            name: "ValidationToolkitTests",
            dependencies: ["ValidationToolkit"],
            path:"Tests")
    ]
)

import PackageDescription

let package = Package(
    name: "ValidationToolkit",
    exclude: ["Tests"]
)

--- 
+++ 
@@ -1,6 +1,21 @@
+// swift-tools-version:4.2
+
 import PackageDescription
 
 let package = Package(
     name: "ValidationToolkit",
-    exclude: ["Tests"]
+    products: [
+        .library(
+            name: "ValidationToolkit",
+            targets: ["ValidationToolkit"])
+    ],
+    targets: [
+        .target(
+            name: "ValidationToolkit",
+            path:"Sources"),
+        .testTarget(
+            name: "ValidationToolkitTests",
+            dependencies: ["ValidationToolkit"],
+            path:"Tests")
+    ]
 )
Update the package manifest file
