Created the library and test targets as well as the executable and library products for the Package file.

Package.swift

@@ -4,18 +4,43 @@ import PackageDescription
 
 let package = Package(
     name: "Colibri",
+    products: [
+        .executable(
+            name: "colibri",
+            targets: ["Colibri"]
+        ),
+        .library(
+            name: "ColibriLibrary",
+            targets: ["ColibriLibrary"]
+        )
+    ],
     dependencies: [
-        .package(url: "https://github.com/apple/swift-argument-parser",
+        .package(
-                 from: "1.0.0")
+            url: "https://github.com/apple/swift-argument-parser",
+            from: "1.0.0"
+        )
     ],
     targets: [
         .executableTarget(
             name: "Colibri",
             dependencies: [
-                .product(name: "ArgumentParser",
+                .product(
-                         package: "swift-argument-parser")
+                    name: "ArgumentParser",
+                    package: "swift-argument-parser"
+                ),
+                .target(name: "ColibriLibrary")
             ],
-            path: "Sources"
+            path: "Sources/Executable"
         ),
+        .target(
+            name: "ColibriLibrary",
+            dependencies: [],
+            path: "Sources/Library"
+        ),
+        .testTarget(
+            name: "ColibriTests",
+            dependencies: ["ColibriLibrary"],
+            path: "Tests/Library"
+        )
     ]
 )

Sources/Executable/Colibri.swift

@@ -1,4 +1,5 @@
 import ArgumentParser
+import ColibriLibrary
 
 @main
 struct Colibri: AsyncParsableCommand {

Sources/Library/ColibriLibrary.swift

@@ -0,0 +1 @@
+import Foundation

Tests/Library/ColibriLibraryTests.swift

@@ -0,0 +1,3 @@
+import Testing
+
+struct ColibriLibraryTests {}