Tests: Ensure no timers are running at the end of each test

This helps fix issues that make tooltip tests sometimes fail when run against
jQuery 3.2 or newer due to timing differences.

This commit adds a function to be attached at `afterEach` & attaches it to
`common.testWidget`.

Author: mgol

tests/lib/common.js

@@ -1,7 +1,8 @@
 define( [
 	"qunit",
-	"jquery" ],
-function( QUnit, $ ) {
+	"jquery",
+	"lib/helper"
+], function( QUnit, $, helper ) {
 
 var exports = {};
 
@@ -66,7 +67,7 @@ function testBasicUsage( widget ) {
 }
 
 exports.testWidget = function( widget, settings ) {
-	QUnit.module( widget + ": common widget" );
+	QUnit.module( widget + ": common widget", { afterEach: helper.moduleAfterEach } );
 
 	exports.testJshint( "/widgets/" + widget );
 	testWidgetDefaults( widget, settings.defaults );

tests/lib/helper.js

@@ -2,7 +2,12 @@ define( [
 	"jquery"
 ], function( $ ) {
 
-var exports = {};
+var exports = {},
+
+	// Store the old count so that we only assert on tests that have actually leaked,
+	// instead of asserting every time a test has leaked sometime in the past
+	oldActive = 0,
+	splice = [].splice;
 
 exports.forceScrollableWindow = function( appendTo ) {
 
@@ -28,6 +33,24 @@ exports.onFocus = function( element, onFocus ) {
 	element.on( "focus", fn )[ 0 ].focus();
 };
 
+/**
+ * Ensures that tests have cleaned up properly after themselves. Should be passed as the
+ * afterEach function on all modules' lifecycle object.
+ */
+exports.moduleAfterEach = function( assert ) {
+
+	// Check for (and clean up, if possible) incomplete animations/requests/etc.
+	if ( jQuery.timers && jQuery.timers.length !== 0 ) {
+		assert.equal( jQuery.timers.length, 0, "No timers are still running" );
+		splice.call( jQuery.timers, 0, jQuery.timers.length );
+		jQuery.fx.stop();
+	}
+	if ( jQuery.active !== undefined && jQuery.active !== oldActive ) {
+		assert.equal( jQuery.active, oldActive, "No AJAX requests are still active" );
+		oldActive = jQuery.active;
+	}
+};
+
 return exports;
 
 } );