How to test your Lambda made in Python locally with serverless

The idea of this tutorial is to quickly and practically demonstrate an example of how to test your lambdas locally

First your machine needs to have Node and Python already configured and then you will need to install serverless globally.

npm i -g serverless

The basic structure of the project will be:

.
├── handler.py
└── serverless.yml

handler.py code

import json
import re


def lambda_handler(event, context):
    informedEmail = json.loads(event)['email']

    result = _validate(informedEmail)

    response = {
        'statusCode': 200,
        'body': result
    }

    return response

def _validate(email: str) -> str:
    emailRegex = '^[a-z0-9]+[\._]?[a-z0-9]+[@]\w+[.]\w{2,3}$'
    if(re.search(emailRegex, email)):  
       return "Valid Email"        

    return "Invalid Email"

The handler.py is basically a very simple code that receives an email in the body json is valid if it really is in the standard of an email through a simple regex

serverless.yml code

service: email-validator

provider:
  name: aws
  runtime: python3.8

functions:
  main:
    handler: handler.lambda_handler

The serverless.yml is the file where you define things like lambda region environment variables and profile used for aws testing.

Important points from our serverless.yml the runtime line where we defined which python version used in the lambda and handler line where we reference the lambda entry point.

Now how do we test our code?

In your terminal of choice, run:

serverless invoke local --data '"{\"email\": \"test@example.com\"}"' --function main

Expected response when we provide a valid email

{
    "statusCode": 200,
    "body": "Valid Email"
}

Congratulations!!

Now you know how to test your lambda locally without any problem