Testing Rake tasks with RSpec examples from the talk I gave at Test Ruby PDX in March 2016. See more here: http://bit.ly/testing-rake-tasks

greeter.rb

class Greeter
  def greet
    puts 'Hello!'
  end
end

rake_spec.rb

require 'rake'
load 'Rakefile'

describe 'Rake tasks' do
  describe 'hello' do
    before { Rake::Task['hello'].reenable }
    
    describe 'features' do
      it 'outputs Hello! to stdout' do
        expect do
          Rake::Task['hello'].invoke
        end.to output("Hello!\n").to_stdout
      end
    end
    
    describe 'units' do
      it 'uses a Greeter to greet' do
        expect(Greeter).to receive_message_chain(
          :new,
          :greet
        )
        Rake::Task['hello'].invoke
      end
    end
  end
end

Rakefile

require_relative 'greeter'

desc 'Outputs a greeting to stdout'
task :hello do
  Greeter.new.greet
end

reenable_example.rb

require 'rake'
load 'Rakefile'

Rake::Task['hello'].invoke
Rake::Task['hello'].reenable
Rake::Task['hello'].invoke