Added test capablities

[matanshukry]

• Added a method in library to add a link to the stream (visibleForTesting)
• Added tests with usage of it

This PR started with my needing a way to test my app in regards to links, but I also ended up adding tests.

[avioli]

I'm sorry to say, but I don't have any time to maintain this package, so it is now marked as discontinued and app_links recommended replacement.