[Zope3-dev] Re: testing interfaces / Cookbook

[Philipp von Weitershausen]

Yuppie,

> The Cookbook uses this example
> 
>     def test_interface(self):
>         self.assert_(IMessageBoard.isImplementedBy(
>             self.makeTestObject()))
> 
> Does it make sense to use providedBy (fka isImplementedBy) in unittests? 

isImplementedBy is deprecated. providedBy should be used when checking 
whether an object *provides* an interface. implementedBy should be used 
when checking whether a class *implements* an interface.

> Wouldn't it be better to verify the interface?

I guess so, though I feel that makes interfaces quite a serious 
contract. Oh well, I guess they *are* a contract, and checking that in 
unit tests couldn't hurt.

However, sometimes you're just interested whether the object you get 
from some machinery implements an interface, i.e. promises a contract. 
That often is enough.

Philipp