The route should work just fine. But you probably don’t want a Slim defined route for the c3 routes. Those are handled by c3.php.
If I understand the documentation for c3 you provided correctly, you need to include the c3.php file at the start of your front controller (index.php):
<?php
require_once __DIR__ . '/vendor/autoload.php';
require_once __DIR__ . '/c3.php'; // c3.php will add the /c3/report/* routes
$app = new \Slim\App();
$app->get('/test', function($request, $response) use ($app) {
// ...
});
$app->run();
Note that if you try to call the /c3/report/* routes using your browser, you will get a 404 error. This is because the route is only handled by c3 if the X_CODECEPTION_CODECOVERAGE header is included in the request. See the debug section in the c3 documentation for instructions on removing this check and enabling debugging.