d6_imagecache_presets reports failure for missing table

The test should rename or drop the ImageCache table, then try to execute the d6_imagecache_presets migration and expect to catch a PDOException. Something like:

$database = get_migration_database()->schema()->dropTable('imagecache_presets');
try {
  $this->executeMigration('d6_imagecache_presets');
  $this->fail('Did not catch expected PDOException.');
}
catch (\PDOException $e) {
  $this->pass('Caught expected PDOException when imagecache_presets table is not present.');
}

One other thing -- we'll need a fail patch, which includes the exception test but NOT the fix -- which will deliberately fail testbot in order to prove that the problem exists. Then we need another patch that includes the test AND the fix, which should pass testbot, in order to prove that the fix fixes the problem :) When all this is here, I will merrily RTBC.

In the meantime, this prevents people from running full-site D6 migrations if they don't have ImageCache installed, so I'm escalating it to Migrate critical.

Actually, ix-nay on that escalation. This problem only breaks the ImageCache migrations.

Fixed!

Frankly, the test is pretty pointless because requirements checking is absolutely not limited to the ImageCache source plugin; it's part of all Migrate Drupal source plugins. However, in the interest of buttering up the committers, we can leave the test in, at least for now, since there is (as far as I know) no other, extensive coverage of checkRequirements().

I'll take your "+1 RTBC" to mean "full-fledged RTBC". :)

A quick reroll, caused by #2533800: Remove all unused use statements from core

Interesting double feature

Pending testbot

Thanks @quietone for pointing me to this issue. I can also confirm it fixes the error for me on a vanilla D6 site with no ImageCache installed.

Nice one, heard someone at DrupalCon raising this issue while trying to test D6 -> D8, glad to see it fixed + test coverage.

Since these changes are self-contained against an experimental module, I believe that makes this eligible for commit during RC. Tagging.

Committed and pushed to 8.0.x. Thanks!