Add more testing stuff

engine/Viewport.ts

@@ -35,7 +35,7 @@ export const viewport: Viewport = {
 	},
 };
 
-export function initViewport(): void {
+export function initViewport(container: HTMLElement = document.body): void {
 	const gameContainer = document.createElement("div");
 	gameContainer.id = "gameContainer";
 
@@ -53,7 +53,7 @@ export function initViewport(): void {
 
 	canvasContainer.appendChild(canvas);
 	gameContainer.appendChild(canvasContainer);
-	document.body.appendChild(gameContainer);
+	container.appendChild(gameContainer);
 }
 
 export function setScale(scale: number): void {