'Check to see if the system-installed version of zope.interface matches
the version requested.  If so, do nothing.  If not, skip the test (if
the desired version is not installed, there is no way to test its
behavior).  If the version of zope.interface cannot be determined
(because pkg_resources is not installed), skip the test.'

def install(self, version):

    try:
        import pkg_resources
    except ImportError as e:
        raise SkipTest(('Cannot    determine    system    version    of    zope.interface:    %s' % (e,)))
    else:
        try:
            pkg = pkg_resources.get_distribution('zope.interface')
        except pkg_resources.DistributionNotFound as e:
            raise SkipTest(('Cannot    determine    system    version    of    zope.interface:    %s' % (e,)))
        installed = pkg.version
        versionTuple = tuple((int(part) for part in installed.split('.')[:len(version)]))
        if (versionTuple == version):
            pass
        else:
            raise SkipTest('Mismatched    system    version    of    zope.interface')
