Test plugin activates successfully

PluginCest.php

<?php
// ...
public function tryActivatingPlugin(AcceptanceTester $I)
{
    // Log in as an administrator.
    $I->loginAsAdmin();
    // Navigate to the plugins page.
    $I->amOnPluginsPage();
    // Attempt to activate the plugin.
    $I->activatePlugin('my-plugin');
    // Verify that the plugin actually activated successfully.  
    $I->seePluginActivated('my-plugin');
}