Issue #2194085 by sun, Berdir: Convert File Managed API tests to DrupalUnitTestBase.

core/includes/file.inc

core/modules/file/lib/Drupal/file/Tests/CopyTest.php

core/modules/file/lib/Drupal/file/Tests/DeleteTest.php

...es/file/lib/Drupal/file/Tests/FileManagedUnitTestBase.php

core/modules/file/lib/Drupal/file/Tests/LoadTest.php

core/modules/file/lib/Drupal/file/Tests/MoveTest.php

core/modules/file/lib/Drupal/file/Tests/SaveDataTest.php

core/modules/file/lib/Drupal/file/Tests/SaveTest.php

core/modules/file/lib/Drupal/file/Tests/SpaceUsedTest.php

core/modules/file/lib/Drupal/file/Tests/UsageTest.php

core/modules/file/lib/Drupal/file/Tests/ValidateTest.php

core/modules/file/lib/Drupal/file/Tests/ValidatorTest.php

...s/simpletest/lib/Drupal/simpletest/DrupalUnitTestBase.php