Question

I’ve written a function which opens a vim editor with the given filename when called.. How can I do the unittest of these types of operations….

Answer 1

To unit test something like this you must mock/stub out your dependencies. In this case lets say you are launching vim by calling os.system(“vim”).

In your unit test you can stub out that function call doing something like:

def launchVim():
    os.system("vim")

def testThatVimIsLaunched():
    try:
        realSystem = os.system
        called = []
        def stubSystem(command):
            if command == "vim":
                called.append(True)
        os.system = stubSystem

        launchVim() # function under test

        assert(called == [True])
    finally:
        os.system = realSystem

For more details on mocking and stubbing take a look at this article

Update: I added the try/finally to restore the original system function as suggested by Dave Kirby