refactor: improve testing setup

spec/setup.ts

@@ -0,0 +1,27 @@
+// SPDX-FileCopyrightText: 2022 Johannes Loher
+//
+// SPDX-License-Identifier: MIT
+
+import en from "../lang/en.json";
+
+function setupStubs() {
+    class StubGame {
+        constructor() {
+            this.i18n = {
+                localize: (key: string) => (key in en ? en[key as keyof typeof en] : key),
+            };
+        }
+        i18n: {
+            localize: (key: string) => string;
+        };
+    }
+
+    const game = new StubGame();
+
+    Object.defineProperties(globalThis, {
+        game: { value: game },
+        Game: { value: StubGame },
+    });
+}
+
+setupStubs();