add tests

This plugin needs tests ... and they might be a bit of fun to write. Many of the main methods don't return anything, or return something but have side effects that are more important. Tests should probably focus on those important side effects.

No files or test entry points are named. Start by locating the plugin's main methods and identifying their important side effects, then inspect the existing test setup if one exists. Done means the key side effects are covered by repeatable tests.

Written by the indexing model from the issue text.