Add unit test for AtomicBox and ObjectCache

Tests/OpenSwiftUICoreTests/Data/Other/AtomicBoxTests.swift

@@ -0,0 +1,22 @@
+//
+//  AtomicBoxTests.swift
+//  OpenSwiftUICoreTests
+
+@testable import OpenSwiftUICore
+import Testing
+
+struct AtomicBoxTests {
+    @Test
+    func expressibleByNilLiteral() {
+        let box: AtomicBox<Int?> = AtomicBox()
+        #expect(box.wrappedValue == nil)
+        box.wrappedValue = 3
+        #expect(box.wrappedValue == 3)
+    }
+
+    @Test
+    func access() {
+        @AtomicBox var box: Int = 3
+        #expect($box.access { $0.description } == "3")
+    }
+}

Tests/OpenSwiftUICoreTests/Data/Other/ObjectCacheTests.swift

@@ -0,0 +1,16 @@
+//
+//  ObjectCacheTests.swift
+//  OpenSwiftUICoreTests
+
+@testable import OpenSwiftUICore
+import Testing
+
+struct ObjectCacheTests {
+    @Test
+    func example() {
+        let cache: ObjectCache<Int, String> = ObjectCache { key in "\(key)" }
+        #expect(cache[0] == "0")
+        #expect(cache[1] == "1")
+        #expect(cache[0] == "0")
+    }
+}