Making Change Happen

Kent Beck describes developer testing as one of the XP practices that can done on your own. In other words, you can do it without any buy-in from the rest of the team.  You can load up JUnit for free and then start testing.
If your code is noticably better, if other people have the tests as a guide to how to change your code, people might get interested.  If there are skeptics, you have to wait for that “teachable moment”- when they have a tricky bug that you can help them fix by writing a test, running the test, making a little change, running the test, repeating until it passes. Little by little, opinion can change that way. Just repeating “we need to do developer testing” doesn't have the same effect.
Working on your own does have disadvantages. Finding a community of people that can help you make the change. Even if you're the only one doing developer testing on your project, reach out across your company, reach out for like-minded individuals.