Restructure test mocks

tests/unit/mocks.ts

@@ -81,15 +81,23 @@ export function createMockCanvasElement(): HTMLCanvasElement {
     const cvs = {
         width: 300,
         height: 200,
-        getContext: vi.fn().mockImplementation(() => ctx ),
+        getContext: () => ctx,
     } as unknown as HTMLCanvasElement;
-    
+
     // @ts-expect-error cannot assign to read only property
     ctx.canvas = cvs;
 
     return cvs;
 }
 
+export function mockCanvasConstructor(): void {
+    vi.spyOn( document, "createElement" ).mockImplementation( type => {
+        if ( type === "canvas" ) {
+            return createMockCanvasElement() as HTMLElement;
+        }
+    });
+}
+
 /**
  * Execute calls debounced by requestAnimationFrame() to use timeouts, which allows
  * us to throttle these with vi.useFakeTimers();

tests/unit/rendering/canvas-elements/layer-sprite.spec.ts

@@ -1,6 +1,6 @@
 import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
 
-import { createMockCanvasElement, createMockZoomableCanvas, mockZCanvas } from "../../mocks";
+import { createMockCanvasElement, createMockZoomableCanvas, mockCanvasConstructor, mockZCanvas } from "../../mocks";
 mockZCanvas();
 
 import { type Store } from "vuex";
@@ -49,11 +49,7 @@ describe( "LayerSprite", () => {
 
     beforeEach(() => {
         vi.useFakeTimers();
-        vi.spyOn( document, "createElement" ).mockImplementation( type => {
-            if ( type === "canvas" ) {
-                return createMockCanvasElement() as HTMLElement;
-            }
-        });
+        mockCanvasConstructor();
 
         layer = LayerFactory.create();