I am looking to apply to a test automation position and on the online application it asks me to attach my resume, but then it has a text box with a caption along the lines of "You can use the following space for a cover letter and any extra information". I have never written a cover letter and I've only had two jobs (one previous to my current position) so I have been able to include most of the information in my resume.
Is it enough to just include my availability and best form of contact (specifically mentioned as part of the "extra information") or should I write a cover letter?. I'm applying for IT jobs in the USA.