Task Validation Debugging I am having issues debugging craft tasks where the issue is caused by validation errors rather than php syntax / environment issues. 

How do you debug validation errors in craft tasks?
Validation errors will still get logged to craft/storage/runtime/logs with a [warning] label.

Other than that, you options are just like you'd debug anything else in PHP.  Preferably with xDebug, but you can always manually Craft::log() and read the log files, too.