Move integration tests to use swift-testing

* Move all tests to use swift-testing
* Add some test skipping traits for OS types, Xcode etc.
* Create a common test module
    * Move the helpers from test source to common test module.
    * TSCBasic requires a minimum os of 10.3, force produce to 13.0
    * Update the IntegrationTests sub package to use the
      common test module.

Author: kcieplak

Diff for: IntegrationTests/Package.swift

@@ -4,11 +4,21 @@ import PackageDescription
 
 let package = Package(
     name: "IntegrationTests",
+    platforms: [.macOS("13.0")],
     targets: [
-        .testTarget(name: "IntegrationTests", dependencies: [
-            .product(name: "SwiftToolsSupport-auto", package: "swift-tools-support-core"),
-            .product(name: "TSCTestSupport", package: "swift-tools-support-core")
-        ]),
+        .testTarget(
+            name: "IntegrationTests",
+            dependencies: [
+                .product(name: "SwiftToolsSupport-auto", package: "swift-tools-support-core"),
+                .product(name: "TSCTestSupport", package: "swift-tools-support-core"),
+                "IntegrationTestSupport",
+            ]),
+        .target(
+            name: "IntegrationTestSupport",
+            dependencies: [
+                .product(name: "TSCTestSupport", package: "swift-tools-support-core"),
+            ]
+        ),
     ]
 )
 

Diff for: IntegrationTests/Sources/IntegrationTestSupport/Filesystem.swift

@@ -0,0 +1,18 @@
+/*
+ This source file is part of the Swift.org open source project
+
+ Copyright (c) 2014 - 2025 Apple Inc. and the Swift project authors
+ Licensed under Apache License v2.0 with Runtime Library Exception
+
+ See http://swift.org/LICENSE.txt for license information
+ See http://swift.org/CONTRIBUTORS.txt for Swift project authors
+ */
+
+import TSCBasic
+
+extension FileSystem {
+    // Returns true if a path does not exist. Makes #expect statements more obvious.
+    public func notExists(_ path: AbsolutePath, followSymlink: Bool = false) -> Bool {
+        !exists(path, followSymlink: followSymlink)
+    }
+}