Let me tell you a story.
In one sunny day, we figure it out that we cannot login on this test account, and also NONE of the clients who wanted to test it.
There was a “well intended” Indian guy that changed the password and the user’s email. Simple and effective, just because he could 🙂
So, we realized that we had to protect the wordpress test user from further modifications, that’s why we created a simple plugin, against vandalism, called WP User Vandalism Protection
This plugin we made it available for free in the WordPress repository. It saved us of a lot of trouble and we hope will help also other developers as well! 🙂