Ruby: Testing Rake Tasks

If you develop in Ruby and you practice Test Driven Development you may consider the question: How do I test Rake tasks?

Let's start with a task that drops each table from a database:

  desc "Wipe the database"
  task :wipe => :environment do
    connection = ActiveRecord::Base.connection
    connection.tables.each do |table|
      begin
        connection.execute("drop table #{table}")
        puts "* dropped table '#{table}'"
      rescue
      end
    end
  end

It may be possible to test this task in it's current form; however, rewriting the task can create a familiar and easily testable class. The key is encapsulating the behavior of the task in a class.

  desc "Wipe the database"
  task :wipe => :environment do
    DatabaseFacade.clean
  end

  class DatabaseFacade
    def self.clean
      connection = ActiveRecord::Base.connection
      connection.tables.each do |table|
        begin
          connection.execute("drop table #{table}")
          puts "* dropped table '#{table}'"
        rescue
        end
      end
    end
  end

After moving the behavior into a class method it's possible to test the class the same as any other class.

class DatabaseFacadeTest < Test::Unit::TestCase
  def test_clean_drops_all_tables
    ActiveRecord::Base.expects(:connection).returns(connection=mock)
    connection.expects(:tables).returns(['table1','table2'])
    connection.expects(:execute).with("drop table table1")
    connection.expects(:execute).with("drop table table2")
    DatabaseFacade.clean
  end
end