We had TDD guru Johannes Brodwall deliver a workshop on TDD and refactoring for my company last Friday, and that prompted me to (yet again) try to get the continuous test runner Infinitest working in IntelliJ. Today I managed to get it working, but it was certainly not thanks to the non-existing documentation!
The key missing part of getting it working after installing the plugin through the IntelliJ plugin wizard is to enable the Infinitest facet for your project. Right click on the project, choose facet, add Infinitest and voila! You now have a new tab called Infinitest.