How to use the chalice.deploy.models.PreCreatedIAMRole function in chalice

def assert_required_roles_created(self, application):
        resources = application.resources
        assert len(resources) == len(self.given)
        functions_by_name = {f.function_name: f for f in resources}
        # Roles that have the same name/arn should be the same
        # object.  If we encounter a role that's already in
        # roles_by_identifier, we'll verify that it's the exact same object.
        roles_by_identifier = {}
        for function_name, expected in self.roles.items():
            full_name = 'appname-dev-%s' % function_name
            assert full_name in functions_by_name
            actual_role = functions_by_name[full_name].role
            expectations = self.roles[function_name]
            if not expectations.get('managed_role', True):
                actual_role_arn = actual_role.role_arn
                assert isinstance(actual_role, models.PreCreatedIAMRole)
                assert expectations['iam_role_arn'] == actual_role_arn
                if actual_role_arn in roles_by_identifier:
                    assert roles_by_identifier[actual_role_arn] is actual_role
                roles_by_identifier[actual_role_arn] = actual_role
                continue
            actual_name = actual_role.role_name
            assert expectations['name'] == actual_name
            if actual_name in roles_by_identifier:
                assert roles_by_identifier[actual_name] is actual_role
            roles_by_identifier[actual_name] = actual_role
            is_autogenerated = expectations.get('autogenerated', False)
            policy_file = expectations.get('policy_file')
            if is_autogenerated:
                assert isinstance(actual_role, models.ManagedIAMRole)
                assert isinstance(actual_role.policy, models.AutoGenIAMPolicy)
            if policy_file is not None and not is_autogenerated:

application = builder.build(config, stage_name='dev')
        # The top level resource is always an Application.
        assert isinstance(application, models.Application)
        assert len(application.resources) == 1
        assert application.resources[0] == models.LambdaFunction(
            resource_name='foo',
            function_name='lambda-only-dev-foo',
            environment_variables={},
            runtime=config.lambda_python_version,
            handler='app.foo',
            tags=config.tags,
            timeout=None,
            memory_size=None,
            deployment_package=models.DeploymentPackage(
                models.Placeholder.BUILD_STAGE),
            role=models.PreCreatedIAMRole('role:arn'),
            security_group_ids=[],
            subnet_ids=[],
            layers=[],
            reserved_concurrency=5,
        )

def lambda_function():
    return models.LambdaFunction(
        resource_name='foo',
        function_name='app-stage-foo',
        deployment_package=None,
        environment_variables={},
        runtime='python2.7',
        handler='app.app',
        tags={},
        timeout=None,
        memory_size=None,
        role=models.PreCreatedIAMRole(role_arn='foobar'),
        security_group_ids=[],
        subnet_ids=[],
        layers=[],
        reserved_concurrency=None,
    )

security_group_ids=['sg1', 'sg2'],
                                    subnet_ids=['sn1', 'sn2'])
        application = builder.build(config, stage_name='dev')

        assert application.resources[0] == models.LambdaFunction(
            resource_name='foo',
            function_name='lambda-only-dev-foo',
            environment_variables={},
            runtime=config.lambda_python_version,
            handler='app.foo',
            tags=config.tags,
            timeout=None,
            memory_size=None,
            deployment_package=models.DeploymentPackage(
                models.Placeholder.BUILD_STAGE),
            role=models.PreCreatedIAMRole('role:arn'),
            security_group_ids=['sg1', 'sg2'],
            subnet_ids=['sn1', 'sn2'],
            layers=[],
            reserved_concurrency=None,
        )

def _create_role_reference(self, config, stage_name, function_name):
        # type: (Config, str, str) -> models.IAMRole
        # First option, the user doesn't want us to manage
        # the role at all.
        if not config.manage_iam_role:
            # We've already validated the iam_role_arn is provided
            # if manage_iam_role is set to False.
            return models.PreCreatedIAMRole(
                role_arn=config.iam_role_arn,
            )
        policy = models.IAMPolicy(document=models.Placeholder.BUILD_STAGE)
        if not config.autogen_policy:
            resource_name = '%s_role' % function_name
            role_name = '%s-%s-%s' % (config.app_name, stage_name,
                                      function_name)
            if config.iam_policy_file is not None:
                filename = os.path.join(config.project_dir,
                                        '.chalice',
                                        config.iam_policy_file)
            else:
                filename = os.path.join(config.project_dir,
                                        '.chalice',
                                        'policy-%s.json' % stage_name)
            policy = models.FileBasedIAMPolicy(

def _create_role_reference(self, config, stage_name, function_name):
        # type: (Config, str, str) -> models.IAMRole
        # First option, the user doesn't want us to manage
        # the role at all.
        if not config.manage_iam_role:
            # We've already validated the iam_role_arn is provided
            # if manage_iam_role is set to False.
            return models.PreCreatedIAMRole(
                role_arn=config.iam_role_arn,
            )
        policy = models.IAMPolicy()
        if not config.autogen_policy:
            resource_name = 'role-%s' % function_name
            role_name = '%s-%s-%s' % (config.app_name, stage_name,
                                      function_name)
            if config.iam_policy_file is not None:
                filename = os.path.join(config.project_dir,
                                        '.chalice',
                                        config.iam_policy_file)
            else:
                filename = os.path.join(config.project_dir,
                                        '.chalice',
                                        'policy-%s.json' % stage_name)
            policy = models.FileBasedIAMPolicy(filename=filename)