Place your custom plugins in ~/.smolder_plugins. They will be loaded in addition to the builtin plugins.
Smolder uses yapsy for our plugin system.
Plugins are comprised of two files: a .yapsy-plugin config file and the plugin python file referenced in the .yapsy file.
The python file is comprised of a Plugin class and a run method, which is expected to call pass_test or fail_test with the pass or failure message on the object it receives when it runs.
A plugin will only be run if the name of the plugin is listed as an outcome in outcomes
Here is an example plugin.