[Python-Dev] PEP 246, redux (original) (raw)

Jim Fulton jim at zope.com
Wed Jan 12 13:45:50 CET 2005

Clark C. Evans wrote:

On Tue, Jan 11, 2005 at 12:54:36PM -0500, Phillip J. Eby wrote: ... | * In my experience, incorrectly deriving an interface from another is the | most common source of unintended adaptation side-effects, not adapter | composition

It'd be nice if interfaces had a way to specify a test-suite that could be run against a component which claims to be compliant. For example, it could provide invalid inputs and assert that the proper errors are returned, etc.

We've tried this in Zope 3 with very limited success. In fact, so far, our attempts have provided more pain than their worth. The problem is that interfaces are usually abstract enough that it's very difficult to write generic tests. For example, many objects implement mapping protocols, but place restrictions on the values stored. It's hard to provide generic tests that don't require lots of inconvenient hooks. There are exceptions of course. Our ZODB storage tests use a generic storage-interface test, but this is possible because the ZODB storage interfaces are extremely concrete.

Jim

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