Documentation: testing guide

Create a 'testing guide' aimed at security professionals with little or no experience with the BEAM platform. The document should provide both background information, with links to relevant resources, and concrete examples of verification tests that show necessary hardening is in place.

Please add any suggestions for topics that we might cover as comments in this ticket.

Start by reviewing the repository structure and the seven comments on this issue to identify existing documentation conventions, suggested topics, and any relevant security-testing resources. Define the guide's location and coverage with the maintainers, then confirm that it includes BEAM background, linked resources, and concrete verification-test examples for hardening.

Written by the indexing model from the issue text.