To answer my own questions above, the answer is Yes, you need to show more than your Test and Go hotel confirmation when applying for an eVisa. I only put the Letter of Confirmation on my eVisa application since you are only allowed to add 1 jpg. This is what I got back from the Thai Embassy.
"In order to complete your visa application, please send the following document in pdf format to email : <snip> Proof of accommodation in Thailand for at least 7 days after your arrival in Thailand."
My question now is what is considered as proof of accommodation when I book my 7 days hotels from hotels.com, agoda, etc.? A print screen of my hotel confirmation email?