Add tests for os(macOS)

Tests/SnapshotTestingHEICTests/SnapshotTestingHEICTests.swift

@@ -1,19 +1,20 @@
-#if os(iOS) || os(tvOS)
 import XCTest
 import SnapshotTesting
 @testable import SnapshotTestingHEIC
 
 final class SnapshotTestingHEICTests: XCTestCase {
 
+#if os(iOS) || os(tvOS)
     var sut: TestViewController!
 
     override func setUp() {
         super.setUp()
         sut = TestViewController()
-//        isRecording = true
+        //        isRecording = true
     }
 
     override func tearDown() {
+        sut = nil
         super.tearDown()
     }
 
@@ -40,6 +41,29 @@ final class SnapshotTestingHEICTests: XCTestCase {
         assertSnapshot(matching: sut, as: .imageHEIC(on: .iPadPro12_9,
                                                      compressionQuality: 0.75))
     }
+#endif
 
-}
+
+#if os(macOS)
+    func test_HEIC_NSView() {
+        // given
+        let view = NSView()
+        let button = NSButton()
+        // when
+        view.frame = CGRect(origin: .zero, size: CGSize(width: 400, height: 400))
+        view.wantsLayer = true
+        view.layer?.backgroundColor = NSColor.blue.cgColor
+        view.addSubview(button)
+        button.frame.origin = CGPoint(x: view.frame.origin.x + view.frame.size.width / 2.0,
+                                      y: view.frame.origin.y + view.frame.size.height / 2.0)
+        button.bezelStyle = .rounded
+        button.title = "Push Me"
+        button.wantsLayer = true
+        button.layer?.backgroundColor = NSColor.red.cgColor
+        button.sizeToFit()
+        // then
+        assertSnapshot(matching: view, as: .imageHEIC)
+    }
 #endif
+
+}