Preconditions:

• Have a blank Symfony project version 3.2.x as installed by Symfony project generator.
• Install PhpUnit 6.0.x with composer using composer require --dev phpunit/phpunit=~6.0.

Steps to reproduce:

1. Run PhpUnit 6 with vendor/bin/phpunit -c .

Actual result:

PHP Fatal error:  Class 'PHPUnit_Framework_TestCase' not found in /home/user/project/vendor/symfony/symfony/src/Symfony/Bundle/FrameworkBundle/Test/KernelTestCase.php on line 23

Expected result:

PHPUnit 6.0.3 by Sebastian Bergmann and contributors.

.                                                                   1 / 1 (100%)

Time: 107 ms, Memory: 12.00MB

OK (1 test, 2 assertions)

Notes:

• It appears the old class name PHPUnit_Framework_TestCase which is used as a parent class of vendor/symfony/symfony/src/Symfony/Bundle/FrameworkBundle/Test/KernelTestCase.php was completely dropped in favor of PSR compatible namespacing in PhpUnit 6 (see this commit).
• The new namespaced class name was introduced in PhpUnit 4.8 5.4 (see changelog).
• Would it be possible to replace the parent class of KernelTestCase with the new namespaced class?