The latest version of Infinitest works well on IDEA 10. Version 5.1.87 can be found here: http://infinitest.github.com/
The version proposed by the plugin wizard is out of date, you need to manually unzip it indefinitely into the IDEA plugins folder. In OSX, the plugins folder can be found by right-clicking the "Intellij", "Show package contents" icon
After unpacking it, launch Intellij and be sure to add Infinitest facet to your project / module.
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