Piwik\Plugin\Manager::isPluginActivated PHP Method

    public function isPluginActivated($name)
    {
        return in_array($name, $this->pluginsToLoad) || $this->doLoadAlwaysActivatedPlugins && $this->isPluginAlwaysActivated($name);
    }

 public function test_deactivatePlugin()
 {
     $this->assertFalse($this->manager->isPluginActivated('ExampleTheme'));
     $this->manager->activatePlugin('ExampleTheme');
     $this->assertTrue($this->manager->isPluginActivated('ExampleTheme'));
     $this->manager->deactivatePlugin('ExampleTheme');
     $this->assertFalse($this->manager->isPluginActivated('ExampleTheme'));
 }