"Interestingness tests" are Python modules that can be imported by Lithium.
They should export a function called
interesting. The first argument to
interesting will be an array of extra command-line arguments passed to Lithium (if any), and the second will be a suggested prefix for temporary files. The function should return True if the input is interesting, and False otherwise. Take care to ensure that input that fails to parse gives False.
Optionally, they can also have a function called "init", which will be called only once with the same array as the first argument to interesting.
Try to design the interestingness test so that the last argument passed will usually be the file the user wants to reduce. But thanks to the --testcase option, you don't have to do this if it doesn't make sense for your test.