How to use the nose2.util.ensure_importable function in nose2

def handleFile(self, event):
        """Load doctests from text files and modules"""
        path = event.path
        _root, ext = os.path.splitext(path)
        if ext in self.extensions:
            suite = doctest.DocFileTest(path, module_relative=False)
            event.extraTests.append(suite)
            return
        elif not util.valid_module_name(os.path.basename(path)):
            return

        name, package_path = util.name_from_path(path)
        util.ensure_importable(package_path)
        try:
            module = util.module_from_name(name)
        except Exception:
            # XXX log warning here?
            return
        if hasattr(module, '__test__') and not module.__test__:
            return
        try:
            suite = doctest.DocTestSuite(module)
        except ValueError:
            # with python <= 3.5, doctest, very annoyingly, raises ValueError
            # when a module has no tests.
            return
        event.extraTests.append(suite)

if not util.valid_module_name(filename):
            # valid Python identifiers only
            return

        evt = events.MatchPathEvent(filename, full_path, pattern)
        result = self.session.hooks.matchPath(evt)
        if evt.handled:
            if not result:
                return
        elif not self._match_path(filename, full_path, pattern):
            return

        if module_name is None:
            module_name, package_path = util.name_from_path(full_path)
            util.ensure_importable(package_path)
        try:
            module = util.module_from_name(module_name)
        except:
            yield loader.failedImport(module_name)
        else:
            mod_file = os.path.abspath(
                getattr(module, '__file__', full_path))
            realpath = os.path.splitext(mod_file)[0]
            fullpath_noext = os.path.splitext(full_path)[0]
            if realpath.lower() != fullpath_noext.lower():
                module_dir = os.path.dirname(realpath)
                mod_name = os.path.splitext(os.path.basename(full_path))[0]
                expected_dir = os.path.dirname(full_path)
                msg = ("%r module incorrectly imported from %r. "
                       "Expected %r. Is this module globally installed?"
                       )

def prepareSysPath(self):
        """Add code directories to sys.path"""
        tld = self.topLevelDir
        sd = self.startDir
        if tld is None:
            tld = sd
        tld = os.path.abspath(tld)
        util.ensure_importable(tld)
        for libdir in self.libDirs:
            libdir = os.path.abspath(os.path.join(tld, libdir))
            if os.path.exists(libdir):
                util.ensure_importable(libdir)

def prepareSysPath(self):
        """Add code directories to sys.path"""
        tld = self.topLevelDir
        sd = self.startDir
        if tld is None:
            tld = sd
        tld = os.path.abspath(tld)
        util.ensure_importable(tld)
        for libdir in self.libDirs:
            libdir = os.path.abspath(os.path.join(tld, libdir))
            if os.path.exists(libdir):
                util.ensure_importable(libdir)