Troubleshoot canvas test warning messages in jest.

Author: seogi1004

jest.config.js

@@ -1,4 +1,5 @@
 module.exports = {
+    "setupFiles": [ "./test/setup.js" ],
     "moduleFileExtensions": [
         "js",
         "json",

package-lock.json

@@ -48,6 +48,7 @@
     "html-webpack-plugin": "^3.2.0",
     "jest": "^23.6.0",
     "jest-serializer-vue": "^2.0.2",
+    "sinon": "^7.2.2",
     "uglifyjs-webpack-plugin": "^1.3.0",
     "vue-jest": "^3.0.0",
     "vue-loader": "^15.4.2",

package.json

@@ -0,0 +1,23 @@
+import sinon from 'sinon';
+
+const createElement = global.document.createElement;
+const FAKECanvasElement = {
+    getContext: jest.fn(() => {
+        return {
+            fillStyle: null,
+            fillRect: jest.fn(),
+            drawImage: jest.fn(),
+            getImageData: jest.fn(),
+        };
+    }),
+};
+
+/**
+ * Using Sinon to stub the createElement function call with the original method
+ * unless we match the 'canvas' argument.  If that's the case, return the Fake
+ * Canvas object.
+ */
+sinon.stub(global.document, 'createElement')
+    .callsFake(createElement)
+    .withArgs('canvas')
+    .returns(FAKECanvasElement);