Lab: Testing Serverless Applications in AWS Development Environments

This lab provides a guided experience in testing AWS Lambda functions and API Gateway endpoints within a dedicated development environment. You will learn to perform local testing, deploy a development stack, and use AWS-native tools to validate application logic.

Prerequisites

Before starting, ensure you have the following:

AWS Account: Access to an AWS account with permissions to create Lambda, API Gateway, and IAM roles.
AWS CLI: Installed and configured with <YOUR_ACCESS_KEY>.
AWS SAM CLI: Installed (sam --version).
Runtime: Python 3.9+ or Node.js 18+ installed locally.

Learning Objectives

By the end of this lab, you will be able to:

Perform local testing of event-driven functions using SAM.
Deploy a serverless stack to a specific 'development' stage.
Create and manage JSON test events in the AWS Lambda Console.
Test API Gateway endpoints using stage variables.

Architecture Overview

The following diagram illustrates the testing workflow and the resources you will provision:

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Step-by-Step Instructions

Step 1: Initialize the Lab Project

We will use the AWS Serverless Application Model (SAM) to bootstrap our testing environment.

bash

sam init --name brainybee-test-lab --runtime python3.9 --app-template hello-world --package-type Zip
cd brainybee-test-lab

[!NOTE] This creates a standard directory structure: hello_world/ for code and template.yaml for infrastructure.

Step 2: Local Testing with JSON Payloads

Before deploying, we test the function locally to ensure logic is correct without incurring cloud costs.

bash

# Generate a mock API Gateway event
sam local generate-event apigateway aws-proxy > event.json

# Invoke the function locally
sam local invoke "HelloWorldFunction" --event event.json

▶Console alternative

Local testing is strictly CLI-based. To test without CLI, you must deploy the code first (see Step 3).

Step 3: Deploy to Development Environment

Now, we deploy the stack to AWS using a 'dev' suffix to keep it isolated from production.

bash

sam deploy --guided --stack-name brainybee-dev-stack

[!IMPORTANT] When prompted for 'Setting default arguments', ensure you set the Stage parameter to dev.

Step 4: Testing via AWS Lambda Console

Once deployed, we use the console to test specific event patterns (Skill 3.3.1).

Navigate to the Lambda Console.
Select your function: brainybee-dev-stack-HelloWorldFunction-....
Click the Test tab.
Click Create new event.
Event name: DevTestEvent.
Template: apigateway-aws-proxy.
Click Save then Test.

Step 5: Validating API Gateway Stages

Confirm that your development endpoint is active and returning the expected payload.

bash

# Replace <API_ID> with the ID from the SAM output
curl https://<API_ID>.execute-api.<YOUR_REGION>.amazonaws.com/Prod/hello/

Checkpoints

Checkpoint	Action	Expected Result
Local Test	Run `sam local invoke`	JSON response with `"statusCode": 200`
Deployment	Check CloudFormation Console	Stack status: `CREATE_COMPLETE`
Integrated Test	Run `curl` command	`{"message": "hello world"}`

Clean-Up / Teardown

To avoid ongoing charges, delete all resources created in this lab.

[!WARNING] Failure to run these commands will result in active resources remaining in your account.

bash

sam delete --stack-name brainybee-dev-stack

Troubleshooting

Error	Possible Cause	Fix
`Runtime.ImportModuleError`	Missing dependencies in package	Run `sam build` before invoking or deploying.
`AccessDenied`	IAM User lacks permissions	Ensure your CLI profile has `PowerUserAccess` or `AdministratorAccess`.
`Docker not running`	Local testing requires Docker	Start Docker Desktop or the `dockerd` service.

Stretch Challenge

Task: Implement a Mock API. Modify the app.py code to check for a header X-Mock-Enabled. If true, return a hardcoded JSON response without processing. Update your event.json and test it locally using sam local invoke.

Cost Estimate

Service	Usage	Estimated Cost
AWS Lambda	< 1,000 requests	$0.00 (Free Tier)
API Gateway	< 1,000 requests	$0.00 (Free Tier)
CloudWatch Logs	< 5GB Storage	$0.00 (Free Tier)
Total		$0.00

Concept Review

Testing in development environments is a critical phase of the CI/CD pipeline.

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Unit Testing: Testing individual components (Lambda logic) in isolation.
Integration Testing: Testing how components interact (API Gateway -> Lambda -> Database).
Stage Variables: Used in API Gateway to point to different Lambda aliases or versions based on the environment (/dev vs /prod).