tests.php

<?php 

    public function testGetCitiesList()
    {

        $getClient = static::createClient([]);

        $getClient->request(
            'GET',
            '/api/v3/cities',
            [],
            [],
            ['HTTP_ACCEPT' => 'application/json']
        );

        $response = $getClient->getResponse();

        $this->assertJsonResponse($response);
        $this->assertJsonResponseContent($response, 'get-cities');

    }
    
       public function testGetCitiesListInItalian()
    {

        $getClient = static::createClient([]);

        $getClient->request(
            'GET',
            '/api/v3/cities',
            [],
            [],
            [
                'HTTP_ACCEPT' => 'application/json',
                'HTTP_ACCEPT-LANGUAGE' => 'it-it,it;q=0.5'
            ]
        );

        $response = $getClient->getResponse();

        $this->assertJsonResponse($response);
        $this->assertJsonResponseContent($response, 'get-cities-it');

    }