Testing a scroll method

I need to test a method called scrollToBottom which does the following:

this.getMainElem().scrollTop = this.getMainElem().scrollHeight;

Since a new element has no scrollHeight or scrollTop value until it has been pasted onto the DOM, how can I test my method? At the moment, I have to create a new element with text, a height and overflow auto then append it directly to document.body.

Can you suggest a cleaner way of testing this?