What tools can be used to help multi-user testing

Question

When developing a website, I often need to test scenarios like this:

When user A logs in, she should see X button while user B can not

And doing this kind of testing requires me to do a lot of log in and log out with different test accounts, which is by no means convenient.

I wonder if there are any tool that can help me do this?

Answer 1

My suggestion would be to use two (or more, if needed) different browsers. They have their own sessions, therefore you can be logged in with both users at the same time.

As example, you can use Internet Explorer for one, and Mozilla Firefox for other user.

Pretty simple!

Update 16th of December, 2016:
Nowadays, when browsers have introduced private sessions (ie. Incognito for Chrome) you can just open this private session and log in with that. It won't use storage mechanisms related with main browser window.
Though, in Chrome, at least - opening two incognito windows won't make you get in total of 3 sessions. The incognitos, all live with a "single" session so to speak. Don't know about Firefox and others.