Fatal error: Cannot redeclare class Drupal\Tests\migrate\Unit\TestMigration

Problem/Motivation

phpunit fails to run tests because of

Fatal error: Cannot redeclare class Drupal\Tests\migrate\Unit\TestMigration in drupal/core/modules/migrate/tests/src/Unit/MigrationTest.php on line 171

Call Stack:
    0.0002     234288   1. {main}() /Users/mkalkbrenner/git/drupal/vendor/phpunit/phpunit/phpunit:0
    0.0091    1106976   2. PHPUnit_TextUI_Command::main() /Users/mkalkbrenner/git/drupal/vendor/phpunit/phpunit/phpunit:47
    0.0091    1107600   3. PHPUnit_TextUI_Command->run() /Users/mkalkbrenner/git/drupal/vendor/phpunit/phpunit/src/TextUI/Command.php:100
    0.0091    1110464   4. PHPUnit_TextUI_Command->handleArguments() /Users/mkalkbrenner/git/drupal/vendor/phpunit/phpunit/src/TextUI/Command.php:111
    0.3329    1951872   5. PHPUnit_Util_Configuration->getTestSuiteConfiguration() /Users/mkalkbrenner/git/drupal/vendor/phpunit/phpunit/src/TextUI/Command.php:649
    0.3329    1953136   6. PHPUnit_Util_Configuration->getTestSuite() /Users/mkalkbrenner/git/drupal/vendor/phpunit/phpunit/src/Util/Configuration.php:870
    3.1698  127304496   7. PHPUnit_Framework_TestSuite->addTestFiles() /Users/mkalkbrenner/git/drupal/vendor/phpunit/phpunit/src/Util/Configuration.php:959
    5.2540  203369248   8. PHPUnit_Framework_TestSuite->addTestFile() /Users/mkalkbrenner/git/drupal/vendor/phpunit/phpunit/src/Framework/TestSuite.php:409
    5.2545  203664512   9. PHPUnit_Util_Fileloader::checkAndLoad() /Users/mkalkbrenner/git/drupal/vendor/phpunit/phpunit/src/Framework/TestSuite.php:335
    5.2545  203664664  10. PHPUnit_Util_Fileloader::load() /Users/mkalkbrenner/git/drupal/vendor/phpunit/phpunit/src/Util/Fileloader.php:38

That happens for example when you run the search_api_solr tests like:
./vendor/bin/phpunit --group search_api_solr_multilingual -c "modules/search_api_solr/phpunit.xml.travis"

The problem is that drupal/core/modules/migrate/tests/src/Unit/MigrationTest.php and drupal/core/modules/migrate/tests/src/Unit/MigrationPluginManagerTest.php both declare the same class \Drupal\Tests\migrate\Unit\TestMigration.

The problem was introduced into 8.2.x and 8.1.x by the commit of #2710133: Follow up to #2561697 - Migration should not choke when the content_node_field table isn't available.

Proposed resolution

Rename class TestMigration to TestMigrationMock in drupal/core/modules/migrate/tests/src/Unit/MigrationPluginManagerTest.php.

Remaining tasks

Test the patch. None.

User interface changes

None.

API changes

None.

Data model changes

None.