Sending push notifications to a user

I have a function whose responsibility is to send a push notification to a user. I call this function from a view in flask framework.

I have read multiple articles around refactoring and good designs but I want to know from those who have been doing this for a while what I can improve.

Here is the function.

 def send_push(api_key, cid, username,request_signature):

        ## ---> DB CALLS
        master_db = get_db('master_db')
        cname = master_db.companies.find_one({'company_id': cid})['company_name']
        company_db = get_db(cname)
        application = company_db.applications.find_one({'app_config.api_key':api_key})


        if not application:
            #error_log_writer(cid=cid, error='API Key is invalid')
            raise InvalidApiKey('The API Key is incorrect.')

        appname = application['app_name']

        # application = company_db.applications.find_one({'app_name': appname})
        username_appname = username + '_' + appname
        redis_db = get_redis()

        ## DB CALLS
        if redis_db.hgetall(username_appname):
            # error_log_writer(cid=cid, error='The PUSH request is already in process', appname=appname)
            raise SomeCustomException(' The request is already in process.')

        auth_id = generate_random_alphanumeric(10)


        from pyfcm import FCMNotification

        push_service = FCMNotification(
            api_key="xxxxx"
            )



        ## DB CALLS
        user = company_db.users.find_one({"_id": username})

        if not user:
            raise UserNotFound


        ## DB CALLS
        registration_id = company_db.users.find_one({"_id": username})['device_token']


        data_message = {
            "Nick" : "Mario",
            "body" : "great match!",
            "app_name": appname,
            "cid": cid,
            "username":username,
            "auth_id" : auth_id,
            "api_key": api_key,
            "request_signature":request_signature
        }
        message_body = "authenticate app?"
        username_appname = username + '_' + appname
        username_appname_response = username_appname + 'response'

        ## DB CALLS
        redis_db.setex(name=username_appname_response, value='waiting', time=180)
        redis_data = {'auth_id': auth_id, 'ts': datetime.datetime.now().strftime('%s')}
        redis_db.hmset(username_appname, redis_data)
        redis_db.expire(username_appname, 180)


        result = push_service.notify_single_device(registration_id=registration_id,  data_message=data_message)

I think this has many code smells. Ideally, I would like to refactor it so that I get

• Easy unit testing
• Avoiding mocks for unit testing where necessary
• Minimal side effects
• Readable code.

Current issues that I think are there:

• Lots of database calls scattered around the core business logic.
• Unit testing is difficult as lots of db calls requires mocking
  them. This tightly couples the test to my implementation rather than behaviour of the function.
• Lots of indirection to logic is introduced because of scattered calls to mongo db & redis.

Possible solutions:

• pass db objects to function rather than creating them inside the function that handles business logic(but this will just defer the object creation to a higher level so db calls will have to be mocked anyways)

How would you refactor this function considering best practices?

Is it a general practice while developing CRUD app to have multiple mocks on average for every function?