In python you can mock pretty much anything you want. You can mock package-defined variables by simply modifying them to the value you want (sys.modules['mymodu

In python you can mock pretty much anything you want. You can mock package-defined variables by simply modifying them to the value you want (sys.modules['mymodule'].MY_GLOBAL_SWITCH = True). In such a way you can even mock standard library functions and built-ins (which have their own __builtin__ package). With such capabilities you can test pretty much any code. (There are some limitations indeed, like you can't change types which are defined in C code.)