def start(self, verifier_id, deployment_id, tags=None, **run_args):
        """Start a verification.
        
        # The check is needed in `rally verify`  command to validate that we can perform
        # all actions on the specific deployment. `rally task` has the same check, so we 
        # do not need to copy that anywhere. 
        deployment = objects.Deployment.get(deployment_id)

        if deployment["status"] != consts.DeployStatus.DEPLOY_FINISHED:
            raise exceptions.DeploymentNotFinishedStatus(
                name=deployment["name"],
                uuid=deployment["uuid"],
                status=deployment["status"])
                
        # In Rally < 0.8.0 there was a tempest context that installs tempest if 
        # needed. https://github.com/openstack/rally/blob/0.7.0/rally/plugins/openstack/context/not_for_production/tempest.py
        # The similar context should be implemented. As for the first version of 
        # implementation, let's implement the simple context that will accept verifier ID and 
        # check that it is already configured, if not - call configure.
        verifier = self.api.verifier._get(verifier_id)
        if verifier.status != consts.VerifierStatus.INSTALLED:
            raise exceptions.RallyException(
                "Failed to start verification because verifier %s is in '%s' "
                "status, but should be in '%s'." % (
                    verifier, verifier.status, consts.VerifierStatus.INSTALLED)
            )

        verifier.set_deployment(deployment_id)
        if not verifier.manager.is_configured():
            self.api.verifier.configure(verifier, deployment_id)

        # It can be ignored for now.
        verifier.manager.validate(run_args)
        
        # we do not need to create Verification object since we will save results 
        # as task results 
        verification = objects.Verification.create(
            verifier_id=verifier_id, deployment_id=deployment_id, tags=tags,
            run_args=run_args)
        LOG.info("Starting verification (UUID=%s) for deployment '%s' "
                 "(UUID=%s) by verifier %s.", verification.uuid,
                 verifier.deployment["name"], verifier.deployment["uuid"],
                 verifier)
        verification.update_status(consts.VerificationStatus.RUNNING)

        context = {"config": verifier.manager._meta_get("context"),
                   "run_args": run_args,
                   "verification": verification,
                   "verifier": verifier}
        try:
            with vcontext.ContextManager(context):
                results = verifier.manager.run(context)
        except Exception as e:
            verification.set_error(e)
            raise

        # TODO(ylobankov): Check that verification exists in the database
        #                  because users may delete verification before tests
        #                  finish.
        verification.finish(results.totals, results.tests)

        LOG.info("Verification (UUID=%s) has been successfully finished for "
                 "deployment '%s' (UUID=%s)!", verification.uuid,
                 verifier.deployment["name"], verifier.deployment["uuid"])

        return {"verification": verification.to_dict(),
                "totals": results.totals,
"tests": results.tests}