RSpec setup for testing rake tasks

rake.rb

# spec/support/rake.rb

require 'rake'

module Rake::TestHelpers
  def run_task(name=subject)
    Rake::Task[name].reenable
    Rake.application.invoke_task name
  end
end

RSpec.configure do |config|
  config.include Rake::TestHelpers, type: :task

  config.before(:each, type: :task) do
    Rake::Task.define_task :environment
    Rake.application.rake_require example.metadata[:task]
  end
end

usage_example.rb

# spec/tasks/admin_spec.rb

require 'spec_helper'

describe task: 'tasks/admin', type: :task do
  before :each { Admin.destroy_all }

  describe 'create' do
    subject { 'admin:create' }

    before { run_task }

    it 'creates one admin' do
      expect(Admin.count).to be 1
    end
  end
end