### Question:
FilePluginManager implements PluginManager { @Override public void addPlugin(AlertPlugin plugin) { pluginMap.put(plugin.getId(), plugin); } FilePluginManager(String dirPath, String[] whitePrefixes, String[] excludePrefixes); @Override AlertPlugin findOne(String pluginId); @Override Map<String, AlertPlugin> findAll(); @Override void addPlugin(AlertPlugin plugin);  }### Answer:
@Test public void addPlugin() { filePluginManager.addPlugin(alertPlugin); assertNotNull(filePluginManager.findAll()); }