Drupal\migrate_drupal\Tests\StubTestTrait is not compatible with PHPUnit 8

Problem/Motivation

Discovered in #3063887: Support PHPUnit 8 optionally in Drupal 8, while keeping support for ^6.5 and ^7.

Drupal\migrate_drupal\Tests\StubTestTrait implements

protected function createStub($entity_type_id)

This method has a name collision with a PHPUnit 8 method on PHPUnit\Framework\TestCase that has a different signature and a different purpose.

This will prevent future usage of PHPUnit 8.

Proposed resolution

• Rename createStub to something else
• Deprecate createStub
• Add/adjust tests

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet