Standardize AppKitBackend CI rendering env's dpi and color space

Credit goes to pointfreeco/swift-snapshot-testing#533

Author: stackotter

.github/workflows/swift-macos.yml

@@ -38,9 +38,3 @@ jobs:
         swift build --target GtkExample
     - name: Test
       run: swift test --test-product swift-cross-uiPackageTests
-    - name: Upload snapshot
-      uses: actions/upload-artifact@v4
-      if: always()
-      with:
-        name: snapshot
-        path: snapshot.tiff

Sources/AppKitBackend/AppKitBackend.swift

@@ -1402,6 +1402,16 @@ class NSSplitViewResizingDelegate: NSObject, NSSplitViewDelegate {
 public class NSCustomWindow: NSWindow {
     var resizeDelegate = ResizeDelegate()
 
+    /// Allows the backing scale factor to be overridden. Useful for keeping
+    /// UI tests consistent across devices.
+    ///
+    /// Idea from https://github.com/pointfreeco/swift-snapshot-testing/pull/533
+    public var backingScaleFactorOverride: CGFloat?
+
+    public override var backingScaleFactor: CGFloat {
+        backingScaleFactorOverride ?? super.backingScaleFactor
+    }
+
     class ResizeDelegate: NSObject, NSWindowDelegate {
         var resizeHandler: ((SIMD2<Int>) -> Void)?
 

Tests/SwiftCrossUITests/SwiftCrossUITests.swift

@@ -68,6 +68,12 @@ final class SwiftCrossUITests: XCTestCase {
         func testBasicLayout() throws {
             let backend = AppKitBackend()
             let window = backend.createWindow(withDefaultSize: SIMD2(200, 200))
+
+            // Idea taken from https://github.com/pointfreeco/swift-snapshot-testing/pull/533
+            // and implemented in AppKitBackend.
+            window.backingScaleFactorOverride = 1
+            window.colorSpace = .genericRGB
+
             let environment = EnvironmentValues(backend: backend)
                 .with(\.window, window)
             let viewGraph = ViewGraph(
@@ -86,11 +92,9 @@ final class SwiftCrossUITests: XCTestCase {
             backend.setSize(of: view, to: result.size.size)
             backend.setSize(ofWindow: window, to: result.size.size)
 
-            try Self.snapshotView(view).write(to: URL(fileURLWithPath: "snapshot.tiff"))
-
             XCTAssertEqual(
                 result.size,
-                ViewSize(fixedSize: SIMD2(94, 95)),
+                ViewSize(fixedSize: SIMD2(88, 95)),
                 "View update result mismatch"
             )