[Tutor] Testing classes with class variables: How best to reset class state between tests?

[Peter Otten]

boB Stepp wrote:

> class MyClass:
>     class_var1 = value1
>     class_var2 = value2
>     ...
> 
>     methods some which may affect class variables
> 
> This is a spinoff of my earlier questions about creating an instance
> counter for a class.  I started to implement this in my actual code
> and started to write tests for the counter.  I quickly realized that
> the counter variable retained state between tests, and, in fact,
> already written tests would now populate the counter before I ever got
> around to the new counter tests.  So how to best deal with this?  Two
> ideas come immediately to mind:
> 
> 1) Use setup and/or teardown methods to manually reset all class
> variables to their desired initial state.  A downside of this is that
> I will have to go back to all previous tests involving this class and
> add these methods.

setUp()/tearDown() seems fine. Put them into a base class that you can 
derive from to avoid repetition.

> 
> 2) Forcibly reloading the import with importlib.reload(myclassmodule).
> This seems like using a sledge hammer to swat a fly.  And it would
> seem that it would have to be done repeatedly and added to earlier
> tests as well.

That's a hack; you can never be sure that you have replaced all objects from 
the previous import.
 
> Does Python provide a better solution?  For the record my test runner
> is currently pytest.

While I think (1) is fine you may also consider pytest's autouse fixtures.