debt - bail out on some window methods in tests

test/electron/renderer.html

@@ -19,9 +19,9 @@
 		// windows. This we cannot allow as it may crash
 		// the test run.
 		// !!! DO NOT CHANGE !!!
-		window.open = function () {return null;};
-		window.alert = function () {}
-		window.confirm = function () {}
+		window.open = function () { throw new Error('window.open() is not supported in tests!'); };
+		window.alert = function () { throw new Error('window.alert() is not supported in tests!'); }
+		window.confirm = function () { throw new Error('window.confirm() is not supported in tests!'); }
 
 		mocha.setup({
 			ui: 'tdd',