Eclipse Mode plugin has an interesting feature to activate the Build on save in IDEA
And the sources are available here (licence to check) :
Can we integrate that in Infinitest ?
Can we try to build on auto-save (Idea does that).
I'm opened to discuss about that.
There is an updated version available here http://plugins.intellij.net/plugin/?idea_ce&id=6643
It works with IntelliJ 11.
When activated, on save, build is done and infinitest kicks in directly.
I haven't tried with auto-save, but if Eclipse Mode works in auto-save, the combination should work as well.
You can use a Macro to save and build. Infinitest will trigger automatically.