Idea: Add test cases to DMs that checks if all remote urls exist

It happens regularly that DMs don't work due to typos in the url of the data source or moving of the source.
Idea: Make a package that can be used in the DM to create a test case that checks if all urls exist using curl or wget.
Could be a student project.

Start by identifying how data managers (DMs) are structured in this repository and where their test cases are defined. Compare whether curl or wget can check each remote URL reliably, then define the package interface and failure behavior. Done means a reusable DM test mechanism exists and demonstrates detection of invalid or moved URLs.

Written by the indexing model from the issue text.