<p>I've used the <a href="http://groups.csail.mit.edu/pag/continuoustesting/" rel="noreferrer">MIT Continuous testing</a> plugin in the past, but it has long since passed out of date and is no longer compatible with anything approaching a modern release of Eclipse. </p>

<p>Does anyone have a good replacement? Free, naturally, is preferred. </p>

There is a list in this Ben Rady article at Object Mentor:
Continuous Testing Explained
.  Unfortunately the only Eclipse tool appears to be
CT-Eclipse
which is not currently maintained either.
There is also
Fireworks
for IntelliJ and
Infinitest
which is not IDE specific but also has some IntelliJ integration.