Gtag func is undefined in tests suits

Fix it so the test can run without it defined

Author: alexander-svendsen

src/Game.test.tsx

@@ -1,8 +1,6 @@
 import * as React from 'react';
 import * as ReactDOM from 'react-dom';
 
-(global as any).gtag = () => undefined;
-
 import Game from './Game';
 
 (window as any).HTMLElement.prototype.scrollIntoView = () => undefined;

src/scenario/main.ts

@@ -30,9 +30,9 @@ function timeDiffInSeconds(): number {
     return Math.floor((new Date().getTime() - startTime.getTime()) / 1000);
 }
 
-const gtag = (global as any).gtag as any;
+const gtag: (a: any, b:any, c:any) => void = (global as any).gtag;
 const tagIt = (action: string) =>
-    gtag('event', action, {
+    !!gtag && gtag('event', action, {
         event_category: 'game',
         event_label: new Date().toUTCString(),
         value: timeDiffInSeconds(),