Stub in migration process plugin does not do complete process

Crappy tests can be deleted yes.

Bah, you shouldn't listen to me :) here's the relevant code from Source

    $source_configuration = $this->migration->get('source');

    while ($this->getIterator()->valid()) {
      $row_data = $this->getIterator()->current() + $source_configuration;
      $this->getIterator()->next();
      $row = new Row($row_data, $this->migration->getSourcePlugin()->getIds(), $this->migration->get('destinationIds'));

therefore the source configuration needs to be added to the values not the ids :/

Invalid argument supplied for foreach()
Drupal\migrate\Plugin\migrate\process\Iterator->transform(NULL, Object, Object, 'filters')
Drupal\migrate\MigrateExecutable->processRow(Object, Array) 
Drupal\migrate\Plugin\migrate\process\Migration->transform(NULL, Object, Object, 'body/format') 

at first look, this means that filters needs a default array in the source (easy) but at second look, is this trying to stub a format?? Didn't we (try to) ban that?

d6_comment and d6_custom_block both depend on d6_filter_format already

See BlockPluginId: ->transform($delta where $delta is boxes.bid and not blocks.bid. The test confused blocks.bid for boxes.bid. Also, custom blocks can't be stubbed since there's a unique index containing info.

As for comments, as the issue summary says, the source for comments.created (timestamp) needs a default. I went with 0.

I am leaving file for others :)

Hrm, file is not failing? Let's try this; the latest fail is trivial to fix.