// tests/SlotsControllerTest.php

class SlotsControllerTest extends TestCase
{
    use DatabaseMigrations;

...
}

// tests/TestCase.php

public function createApplication()
{
    $app = require __DIR__ . '/../bootstrap/app.php';

    putenv('DB_DEFAULT=testing');
    putenv('DB_DATABASE=testing');
    putenv('DB_CONNECTION=testing');

    $app->make(Illuminate\Contracts\Console\Kernel::class)->bootstrap();

    return $app;
}

public function setUp()
{
    parent::setUp();
    Artisan::call('migrate');
}

public function tearDown()
{
    Artisan::call('migrate:reset');
    parent::tearDown();
    if (class_exists('Mockery')) {
        m::close();
    }
}

// phpunit.xml

<php>
    <env name="APP_ENV" value="testing"/>
    <env name="DB_CONNECTION" value="testing"/>
    <env name="DB_DATABASE" value="testing"/>
    <env name="DB_DEFAULT" value="testing"/>
    <env name="CACHE_DRIVER" value="array"/>
    <env name="SESSION_DRIVER" value="array"/>
    <env name="QUEUE_DRIVER" value="sync"/>
    <env name="MAIL_DRIVER" value="log"/>
</php>

//config/database.php

'connections' => [
    'testing' => [
        'driver' => 'mysql',
        'host' => env('DB_HOST', 'localhost'),
        'port' => env('DB_PORT', '3306'),
        'database' => 'testing',
        'username' => 'testing',
        'password' => 'testing',
        'charset' => 'utf8',
        'collation' => 'utf8_unicode_ci',
        'prefix' => '',
        'strict' => false,
        'engine' => null,
    ],
],


// .env

APP_ENV=local
APP_DEBUG=true
APP_LOG_LEVEL=debug

DB_HOST=127.0.0.1
DB_DATABASE=main
DB_USERNAME=homestead
DB_PASSWORD=secret