How can I debug/test my custom migrate module? I've written a custom migrate module in Drupal 8. (Based on these instructions: https://github.com/wunderkraut/migrate_source_example/)

The migration reads data from a XML file with the "migrate_source_xml" extension and should write/update the data in a node.

I have a yml config file in /config/install/ and some logic in /src/migrate/source/

When I run the migration with "drush mi --all" I get the correct values in my prepareRow function. Unfortunately, no nodes were create and I get the message "Processed 0 items (0 created, 0 updated, 0 failed, 0 ignored)"

With the prepareRow function I'm able to stop the script at this position. But how can I debug the script afterwards? Does exist a postImport function or something similar?

How do you test your D8 migrations?

Thank you very much for your inputs!
The place you want to step through is the while loop in MigrateExecutable::import() - this is where each source row is received after prepareRow(), run through the processing pipeline ($this->processRow), and saved to the destination plugin ($destination->import()).