Which combination of actions will meet these requirements with the LEAST development overhead?

Explanations:

Writing custom unit tests against thecdk.outfile introduces unnecessary complexity and overhead, as the output file is generated from synthesized constructs rather than the constructs themselves. This method may lead to brittle tests that are difficult to maintain.

Using the CDK assertions module allows for direct unit testing of the CDK constructs in a straightforward manner. This approach integrates seamlessly with the CDK and provides a simple way to validate the infrastructure code directly, ensuring that critical configurations are correctly set. Running these tests in a CI/CD pipeline ensures automated validation on commits, which meets both requirements effectively.

Utilizing the CDK runtime context for validation does not directly address the need for unit tests. While it may help enforce specific conditions during synthesis, it does not provide a comprehensive mechanism for testing the configurations of the constructs themselves, making it less effective for validation purposes.

Writing a script to search for configuration strings may identify some security violations, but it lacks the structured approach that CDK assertions provide. This method would likely be less comprehensive and could lead to missed configurations or violations, thus increasing the potential for errors.

The CDK Aspects class can be used to create rules that automatically apply to all constructs within a CDK application. This approach can enforce security best practices and fail stack synthesis if violations are found, aligning well with the requirement to validate configurations in a systematic manner while keeping development overhead low.