The plugin's unit tests fail. This seems to have three causes.
First off, since the test script has to be copied from the plugin's test folder to the project's one the $sf_root_dir is defined incorrectly.
Then the test script is not able to get a database connection, failing with "No connection params set for default", even if a default database is defined.
Thirdly the objects created by _create_object() and _create_object_2() are not modified after creation and thus not saved so they cannot be retrieved afterwards so no tag operations can be performed on them. A simple fix is to just modify any column / property of the objects which of course requires that they have another colum besides their id.
I have attached a patch that fixes these issues as long as the test classes ("Post" and "Link" by default) have a "name" column.