Maintenance: Add unit test coverage

[jeromevdl]

Summary

Add unit test coverage to get a better visibility on where we can have issues, and improve the coverage where needed.

Why is this needed?

Lambda Powertools for Java has a decent amount of unit tests but we don't have a clear view on what is well-tested and more important where we can improve. Having the coverage reports will help driving the effort and make sure we minimize the risk of issues.

Which area does this relate to?

Tests

Solution

We could use one of the standard frameworks (Jacoco, Cobertura) and deploy the reports to codecov.io just like the Python version does (see https://github.com/awslabs/aws-lambda-powertools-python/blob/79e7b4392a1a0f69bcf627b137c81be45867c587/.github/workflows/python_build.yml#L55)

Acknowledgment

• This request meets Lambda Powertools Tenets
• Should this be considered in other Lambda Powertools languages? i.e. Python, TypeScript

[scottgerring]

The powertools for python dashboard is visible here

[jeromevdl]

closed with #1094