PhpUnit error guessing kernel directory

This is my PhpUnit test class:

<?phpnamespace tests\AppBundle\Controller;use Symfony\Bundle\FrameworkBundle\Test\WebTestCase;class SendEmailControllerTest extends WebTestCase{    public function testMailIsSentAndContentIsCorrect()    {        $client = static:: createClient();        ...    }}

But when I try to run it, I get the error whose trace is:

Unable to guess the Kernel directory. C:\myProject\vendor\symfony\symfony\src\Symfony\Bundle\FrameworkBundle\Test\KernelTestCase.php:62 C:\myProject\vendor\symfony\symfony\src\Symfony\Bundle\FrameworkBundle\Test\KernelTestCase.php:138 C:\myProject\vendor\symfony\symfony\src\Symfony\Bundle\FrameworkBundle\Test\KernelTestCase.php:184 C:\myProject\vendor\symfony\symfony\src\Symfony\Bundle\FrameworkBundle\Test\KernelTestCase.php:165 C:\myProject\vendor\symfony\symfony\src\Symfony\Bundle\FrameworkBundle\Test\WebTestCase.php:33 C:\myProject\tests\AppBundle\Controller\SendEmailControllerTest.php:12ERRORS!Tests: 1, Assertions: 0, Errors: 1.Remaining deprecation notices (3)  1x: Using the KERNEL_DIR environment variable or the automatic guessing based on the phpunit.xml / phpunit.xml.dist file location is deprecated since Symfony 3.4. Set the KERNEL_CLASS environment variable to the fully-qualified class name of your Kernel instead. Not setting the KERNEL_CLASS environment variable will throw an exception on 4.0 unless you override the :createKernel() or :getKernelClass() method.    1x in SendEmailControllerTest::testMailIsSentAndContentIsCorrect from tests\AppBundle\Controller  1x: The Symfony\Bundle\FrameworkBundle\Test\KernelTestCase::getPhpUnitXmlDir() method is deprecated since Symfony 3.4 and will be removed in 4.0.    1x in SendEmailControllerTest::testMailIsSentAndContentIsCorrect from tests\AppBundle\Controller  1x: The Symfony\Bundle\FrameworkBundle\Test\KernelTestCase::getPhpUnitCliConfigArgument() method is deprecated since Symfony 3.4 and will be removed in 4.0.    1x in SendEmailControllerTest::testMailIsSentAndContentIsCorrect from tests\AppBundle\ControllerC:\xampp\php\php.exe C:/myProject/vendor/phpunit/phpunit/phpunit --no-configuration tests\AppBundle\Controller\SendEmailControllerTest C:\myProject\tests\AppBundle\Controller\SendEmailControllerTest.php --teamcityTesting started at 23:09 ...PHPUnit 5.6.0 by Sebastian Bergmann and contributors.Process finished with exit code 2

But the problem is that I don't understand how to fix the deprecation issues indicated in the trace...

Edit:

Following the official documentation, I've added the in the phpunit.xml.dist

<?xml version="1.0" encoding="UTF-8"?><!-- https://phpunit.de/manual/current/en/appendixes.configuration.html --><phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"         xsi:noNamespaceSchemaLocation="http://schema.phpunit.de/4.8/phpunit.xsd"         backupGlobals="false"         colors="true"         bootstrap="vendor/autoload.php"><php><ini name="error_reporting" value="-1" /><env name="KERNEL_CLASS" value="App\Kernel" /><server name="KERNEL_CLASS" value="AppKernel" /></php><testsuites><testsuite name="Project Test Suite"><directory>tests</directory></testsuite></testsuites><filter><whitelist><directory>src</directory><exclude><directory>src/*Bundle/Resources</directory><directory>src/*/*Bundle/Resources</directory><directory>src/*/Bundle/*Bundle/Resources</directory></exclude></whitelist></filter></phpunit>

However:

1) I still get the same error

2) The code http://schema.phpunit.de/4.8/phpunit.xsd appears in red, with the message "URI is not registered (Settings | Languages & Frameworks | Schemas and DTDs). So I went to that place and in "External Schemas and DTDs" I added that URI, and the location being my project root. However, this red warning persists and I suspect it is related to the location, but where is it?