Yes, as long as the tests are to test the application as such.
To clarify what I mean: At the place where I am, we restore production to two test environments daily. These environments are for troubleshooting, and in one of the environments also to test the most recent build of the application. So far, we are in the realm of Developer Edition. However, some users also test advanced configuration changes in these environments to see the consequences on a business level, before they do them in production. This is, in my opinion, production and beyond the realm of Developer Edition. (We are not cheating. We have Standard Edition in these environments.)
I also need to clarify that this is a technical forum, and you cannot get authoritative answers about licensing here. To that end, you need to talk to a Microsoft representative. Your question is a common one, and one of the few licensing question I dare answering with confidence. But, nevertheless, if a license auditor would say that you are abusing your Developer Edition, pointing to my amateur post will carry very little weight.