Support for PHPUnit 4 has been removed

Drupal 8.8.0 will require PHP 7, and will no longer support PHPUnit 4.x.; it will only use PHPUnit ^6.5 for testing.

As an effect of this,

1. The drupal-phpunit-upgrade and drupal-phpunit-upgrade-check composer commands were no longer needed and have been removed.
2. The methods getMock and setExpectedException, that provided a BC layer for test code to work on PHPUnit 4, are deprecated and should not be used any longer. They will be removed in Drupal 9. The backwards-compatibility layer method Drupal\Tests\PhpunitCompatibilityTrait::createMock was removed completely.
   • For getMock, replace with PHPUnit\Framework\TestCase::createMock() or getMockBuilder()
   • For setExpectedException, replace all calls with $this->expectException and $this->expectExceptionMessage.
3. Usage of old style PHPUnit class names (e.g. \PHPUnit_Framework_AssertionFailedError), that is provided as a FC layer for PHPUnit 4 test code to work in PHPUnit 6, is now deprecated. Test developers should instead import the fully namespaced class from PHPUnit with

   use PHPUnit\Framework\AssertionFailedError;

   and then use [classname]::class to refer to the class in code

   $this->expectException(AssertionFailedError::class);