I want to run PHPUnit 6.0. * tests in PhpStorm. But this shows me the following error when I want to run tests of one class: "Test class is not specified or is invalid."

I downloaded PHPUnit using Composer. Here is the content composer.json:
{
"require": {
"phpunit/phpunit": "6.0.0"
}
}
Running a test on the command line works. Output:
/usr/bin/php7.1 /path/to/project/vendor/phpunit/phpunit/phpunit --no-configuration MyTestTest /path/to/project/Tests/MyTestTest.php
PHPUnit 6.0.0 by Sebastian Bergmann and contributors.
. 1 / 1 (100%)
Time: 29 ms, Memory: 2.00MB
OK (1 test, 1 assertion)
Additional Information:
- PhpStorm Settings:
- PHP language level: 7.1
- CLI Interpreter: 7.1
- PHPUnit uses Composer autoloader (link to autoload.php)
- PhpStorm Version: 2016.3.3
Tested with 6.0.0 and 6.0.10. Assume all versions are 6.0. * Affected.
5.7.17 ( 6.0.0), .
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