PHPUnit: Why doesn't PHP get ENV variable from phpunit.xml?

Question

PHP

I fasten testing for PHP code.
I check in PhpStorm IDE. The tests are working.
But I can't pass a variable from phpunit.xml to php.
Here is the content of phpunit.xml:

<?xml version="1.0" encoding="UTF-8"?>
<phpunit colors="true" bootstrap="vendor/autoload.php">
    <testsuites>
        <testsuite name="Tests">
            <directory>./tests/</directory>
        </testsuite>
    </testsuites>
    <php>
        <env name="UNIT_TEST" value="true" />
    </php>
</phpunit>

Here is the bootstrap code: (loaded by autoloader)

<?php
define('APP_DIR', __DIR__);
define('BASE_DIR', dirname(APP_DIR));
define('CONFIGS_DIR', APP_DIR . '/configs');
define('VENDOR_DIR', BASE_DIR . '/vendor');
define('CACHE_DIR', BASE_DIR . '/cache');

var_dump(getenv('UNIT_TEST')); //return FALSE
var_dump($_ENV['UNIT_TEST']); //return NULL

Nifiga is not dumped by UNIT_TEST.
What's wrong?
UPD: Tests use parameters from phpunit.xml. Variables are simply ignored.