On Wed, 04 Jul 2012 10:42:56 +0100, andrea crotti wrote: > I'm writing a program which has to interact with many external > resources, at least: > - mysql database > - perforce > - shared mounts > - files on disk > > And the logic is quite complex, because there are many possible paths to > follow depending on some other parameters. This program even needs to > run on many virtual machines at the same time so the interaction is > another thing I need to check... > > Now I successfully managed to mock the database with sqlalchemy and only > the fields I actually need, but I now would like to simulate also > everything else. > > I would like for example that if I simulate I can pass a fake database, > a fake configuration and get the log of what exactly would happen. But > I'm not sure how to implement it now.. One possibility would be to have > a global variable (PRETEND_ONLY = False) that if set should be checked > before every potentially system-dependent command.
I think a better way would be to use a mock database, etc. For each thing which you want to simulate, create a class that has the same interface but a simulated implementation. Then, have your code accept the thing as an argument. E.g. instead of having a hard-coded database connection, allow the database connection to be set (perhaps as an argument, perhaps as a config option, etc.). There are libraries to help with mocks, e.g.: http://garybernhardt.github.com/python-mock-comparison/ > For example > > copytree(src, dest) becomes: > if not PRETEND_ONLY: > copytree(src, dest) Ewww :( Mocking the file system is probably the hardest part, because you generally don't have a "FileSystem" object available to be replaced. In effect, your program has one giant global variable, the file system. Worse, it's not even a named variable, it's hard-coded everywhere you use it. I don't know of any good solution for that. I've often thought about it, but don't have an answer. I suppose you could monkey-patch a bunch of stuff: if ONLY_PRETEND: open = my_mock_open copytree = my_mock_copytree # etc. main() # run your application but that would also be painful. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
