Tutorial: AWS Certified Developer - Associate (DVA-C02)

Unit testing

Concepts

AWS provides a range of services that facilitate effective unit testing practices. These services enable developers to write, execute, and automate tests, ensuring that the application components deployable in the AWS environment are reliable and bug-free.

Key AWS Services for Unit Testing

AWS CodeBuild: A fully managed build service that compiles source code, runs tests, and produces software packages that are ready to deploy.
AWS Lambda: For serverless applications, unit tests can be written for the individual Lambda functions to verify their behavior.
Amazon API Gateway: When using API Gateway to create and deploy APIs, developers can write unit tests for the underlying Lambda functions or HTTP endpoints.

Frameworks for Unit Testing in AWS

In the context of AWS, developers often use testing frameworks that are language-specific. For example:

JUnit for Java applications.
NUnit or xUnit for .NET applications.
pytest or unittest for Python.
Mocha, Jest, or Jasmine for Node.js applications.

These frameworks can be configured in CI/CD pipelines using AWS CodePipeline along with AWS CodeBuild to automate the running of unit tests.

Example: Unit Testing AWS Lambda Functions

Consider an AWS Lambda function written in Node.js. The function might look like this:

exports.handler = async (event) => {
let responseMessage = ‘Hello, ‘ + event.name + ‘!’;

const response = {
statusCode: 200,
body: JSON.stringify({ message: responseMessage }),
};
return response;
};

A unit test for this function using Jest would look something like this:

const lambdaFunction = require(‘./index’);
const event = {
name: ‘World’
};

test(‘The Lambda function returns the correct response object’, async () => {
const result = await lambdaFunction.handler(event);
const expectedResult = {
statusCode: 200,
body: JSON.stringify({ message: ‘Hello, World!’ })
};

expect(result).toEqual(expectedResult);
});

Best Practices for Unit Testing

When preparing for the DVA-C02 exam, it is important to adhere to best practices for unit testing:

Isolation: Unit tests should test a single “unit” of code (e.g., a function or method) in isolation from other parts of the system.
Mocking/Stubs: Use mocking frameworks to simulate external dependencies or services that are not being tested.
Automation: Incorporate unit tests into the AWS CI/CD pipeline for automatic execution upon code commits.
Coverage: Strive for high test coverage but prioritize testing the critical paths of code.
Readability: Write clear and understandable tests, as they serve as documentation for the expected behavior of the system.
Maintainability: Update tests as the system evolves to ensure they remain relevant.

Conclusion

While unit testing is not a service-specific topic for the AWS Certified Developer – Associate (DVA-C02) exam, understanding its application within the AWS context is important. Developers should be familiar with AWS services that support CI/CD, the selected programming language’s unit testing frameworks, and the best practices of unit testing to ensure high-quality, reliable applications in the cloud.

Answer the Questions in Comment Section

True/False: Unit testing in AWS is performed after deploying the application to an AWS environment to validate the cloud infrastructure.

A) True
B) False

Answer: B) False

Explanation: Unit tests are typically performed before deployment to test individual parts of the application code, not the cloud infrastructure. They are often done in the developer’s local environment.

True/False: AWS X-Ray can be used to assist with unit testing by providing insights into how your application and its underlying services are performing.

A) True
B) False

Answer: A) True

Explanation: AWS X-Ray helps developers analyze and debug production, distributed applications, such as those built using a microservices architecture. While not a unit testing tool, it can assist in identifying issues that could inform unit tests.

Which AWS service is a managed source control service that hosts Git-based repositories and can be used to trigger unit test workflows?

A) AWS Lambda
B) Amazon EC2
C) AWS CodeCommit
D) Amazon S3

Answer: C) AWS CodeCommit

Explanation: AWS CodeCommit is a version control service that can host Git repositories and be integrated with other AWS services to automate workflows including running unit tests.

True/False: AWS CodeBuild can be used to automatically run unit tests and provide reports on the results as part of the CI/CD process.

A) True
B) False

Answer: A) True

Explanation: AWS CodeBuild is a fully managed build service that compiles source code, runs tests, and produces software packages. It can be configured to run unit tests and output test reports.

Which of the following AWS tools integrates with AWS CodeCommit to enable continuous integration and unit test execution?

A) AWS CloudFormation
B) AWS CodePipeline
C) Amazon RDS
D) Amazon CloudWatch

Answer: B) AWS CodePipeline

Explanation: AWS CodePipeline is a continuous delivery service that automates the build, test, and deploy phases of your release process. It can integrate with AWS CodeCommit to enable CI workflows, including running unit tests.

True/False: Unit tests should cover both positive and negative test cases to ensure robust code functionality.

A) True
B) False

Answer: A) True

Explanation: Good unit tests should include both positive and negative cases to fully ensure that the code handles various inputs and scenarios correctly.

In the context of AWS Lambda, what best describes the purpose of unit testing?

A) Testing the integration between Lambda functions and API Gateway
B) Testing individual Lambda functions in isolation from AWS services
C) Testing the end-to-end flow of an application
D) Monitoring the performance of deployed Lambda functions

Answer: B) Testing individual Lambda functions in isolation from AWS services

Explanation: Unit testing for AWS Lambda involves testing the Lambda function code in isolation, without dependencies on other AWS services.

When using AWS CodeBuild to run unit tests, which file contains definitions of build commands and test executions?

A) Dockerfile
B) buildspec.yml
C) serverless.yml
D) template.yaml

Answer: B) buildspec.yml

Explanation: AWS CodeBuild uses the buildspec.yml file for specifying build commands and settings, including the execution of unit tests.

True/False: Unit testing frameworks like JUnit and NUnit can easily be integrated with AWS Developer Tools such as AWS CodeBuild and AWS CodePipeline.

A) True
B) False

Answer: A) True

Explanation: Popular unit testing frameworks, such as JUnit (for Java) and NUnit (for .NET), can be incorporated within build and test processes set up in AWS CodeBuild and AWS CodePipeline.

Can unit testing be performed locally for AWS Lambda functions?

A) Yes, by simulating the AWS runtime environment locally
B) No, Lambda functions can only be tested in the AWS cloud
C) Yes, but only using AWS-provided SDKs
D) No, because Lambda functions need to access other AWS services

Answer: A) Yes, by simulating the AWS runtime environment locally

Explanation: AWS Lambda functions can be tested locally by simulating the AWS Lambda runtime environment, using tools such as AWS SAM CLI or the AWS SDKs and mock services.

True/False: Larger units of an application, such as multiple interacting components, are typically tested during unit testing.

A) True
B) False

Answer: B) False

Explanation: Unit testing focuses on the smallest parts of an application, typically individual functions or methods, rather than on interactions between larger components, which are tested during integration testing.

What is a common practice to ensure that unit tests can run quickly and are not dependent on external elements?

A) Testing on the production environment
B) Utilizing test doubles such as mocks, fakes, and stubs
C) Running tests in parallel on multiple EC2 instances
D) Increasing the available memory and CPU for the testing environment

Answer: B) Utilizing test doubles such as mocks, fakes, and stubs

Explanation: Test doubles like mocks, fakes, and stubs are used to mimic the behavior of complex, real objects to ensure unit tests run quickly and are isolated from external dependencies.