This is whitebox test scripting tool for Python. The idea is to totally rip the function being tested out of context and mock it's entire universe in a script. All of the function's global name space and class name space are gutted (including recursive calls to itself) and replaced by mock objects that simply follow along in the script (no need to explicitly create and configure each mock). Even the "self" object passed to methods is mocked in the script.

This allows you to easily simulate anything that you want to (network disconnects, disk full, hardware failures, etc) and see how your code reacts to it. It also lets you completely test a function before other functions it depends on are written.