This week I've been working on a client project where I needed to import a massive XML dataset into a database.  The XML was non-standard and broke its own rules in several places.  Consequently my rake task quickly become very complicated and I needed some tests to ensure I wasn't breaking previous work.  This leads to a rather interesting question: how do you test rake tasks?  After a bit of googling I found a rather neat solution of simply pulling out the rake code to a class. For example, rather than:

desc "Import the XML" 
task :import => :cleanup do   
  File.open(XML_FILE) do |file|     
  # Do importing here...   
end 
end

do something more like

desc "Import the XML" 
task :import => :cleanup do
   File.open(XML_FILE) do |file|
     XMLImporter.parse_lines(file)
   end 
end

XMLImporter can then be tested in the normal way. Good ruby - clean and effective.