[wishlist] Gwibber would benefit from a test suite

Currently we have close to zero test coverage in Gwibber. A basic framework exists with run-tests and ./tests but it is far from ideal.

We should start building up tests in ./tests for each of the supported microblog formats e.g., containing example RSS, JSON etc. output and ensuring parsing into Message objects occurs as expected. These can then be updated as any changes are made to the API etc.

Similarly, when bugs are found with unusual input breaking Gwibber, we should append this to the collection of example input so that we don't regress in the future.