Tests: Keep test iframes around for assertions

Ref 44f8239d3f
Ref gh-2644
Ref gh-2390

test/data/testinit.js

@@ -252,9 +252,9 @@ this.testIframeWithCallback = function( title, fileName, func ) {
 			setTimeout( function() {
 				this.iframeCallback = undefined;
 
-				iframe.remove();
 				func.apply( this, args );
 				func = function() {};
+				iframe.remove();
 
 				done();
 			} );