Try to display informations about a layer if its setup has failed

[Jonathan Ballet]

If a layer fails to execute, zope.testrunner displays in its summary some not very interesting messages:

        Tests with errors:
            runTest (zope.testrunner.runner.SetUpLayerFailure)
            runTest (zope.testrunner.runner.SetUpLayerFailure)
            runTest (zope.testrunner.runner.SetUpLayerFailure)
        Total: ...

I made a patch to allow the SetUpLayerFailure to display something more useful, if the underlying layer supports it. It now calls the _str__ method of the layer object which has failed, which produces something like this:

        Tests with errors:
            Layer: some.tests.layer1
        Total: ...

I also plan to make a patch on zope.app.testing's functional ZCML layer to display the name of the ZCML file of the layer in its __str__, in order to have something like:

        Tests with errors:
           Layer: /foo/bar/baz/ftesting.zcml
           Layer: /flip/flap/flop/ftesting.zcml
        Total: ...

[Tres Seaver (tseaver)]

This patch looks very reasonable.

[Tres Seaver (tseaver)]

Thanks very much for the patch. I have committed it to the trunk for the zope.testrunner 4.0 release.