Automate local integration tests with AWS SAM

While you can use Introduction to testing with sam local invoke to manually test code, AWS SAM also lets you to test your code using automated integration testing. Integration testing helps you detect issues early in the development cycle, improve the quality of your code, and save time while reducing costs.

To author automated integration tests in AWS SAM, you first run tests against local Lambda functions before deploying to the AWS Cloud. The Introduction to testing with sam local start-lambda command starts a local endpoint that emulates the Lambda invoke endpoint. You can invoke it from your automated tests. Because this endpoint emulates the Lambda invoke endpoint, you can write tests once, and then run them (without any modifications) against the local Lambda function, or against a deployed Lambda function. You can also run the same tests against a deployed AWS SAM stack in your CI/CD pipeline.

This is how the process works:

1. Start the local Lambda endpoint.

   Start the local Lambda endpoint by running the following command in the directory that contains your AWS SAM template:

   sam local start-lambda

   This command starts a local endpoint at http://127.0.0.1:3001 that emulates AWS Lambda. You can run your automated tests against this local Lambda endpoint. When you invoke this endpoint using the AWS CLI or SDK, it locally executes the Lambda function that's specified in the request, and returns a response.

2. Run an integration test against the local Lambda endpoint.

   In your integration test, you can use the AWS SDK to invoke your Lambda function with test data, wait for response, and verify that the response is what you expect. To run the integration test locally, you should configure the AWS SDK to send a Lambda Invoke API call to invoke the local Lambda endpoint that you started in previous step.

   The following is a Python example (the AWS SDKs for other languages have similar configurations):

   import boto3
   import botocore
   
   # Set "running_locally" flag if you are running the integration test locally
   running_locally = True
   
   if running_locally:
   
       # Create Lambda SDK client to connect to appropriate Lambda endpoint
       lambda_client = boto3.client('lambda',
           region_name="us-west-2",
           endpoint_url="http://127.0.0.1:3001",
           use_ssl=False,
           verify=False,
           config=botocore.client.Config(
               signature_version=botocore.UNSIGNED,
               read_timeout=15,
               retries={'max_attempts': 0},
           )
       )
   else:
       lambda_client = boto3.client('lambda')
   
   
   # Invoke your Lambda function as you normally usually do. The function will run
   # locally if it is configured to do so
   response = lambda_client.invoke(FunctionName="HelloWorldFunction")
   
   # Verify the response
   assert response == "Hello World"

   You can use this code to test deployed Lambda functions by setting running_locally to False. This sets up the AWS SDK to connect to AWS Lambda in the AWS Cloud.