simpler rake task testing

thoughtbot wrote this interesting post on testing rake tasks. inspired by this, i dug into the rake source code and came up with this simpler approach.

shared_context 'rake' do
  require 'rake'
  let(:rake)      { Rake::Application.new }
  let(:task_name) { self.class.top_level_description }
  let(:task_path) { "lib/tasks/#{task_name.split(":").first}" }
  subject         { rake[task_name] }

  around do |example|
    Rake.with_application(rake) do
      Rails.application.load_tasks
      subject.prerequisites.each do |prerequisite|
        rake[prerequisite].clear
      end
      example.run
    end
  end
end

the generic part of my test is like so:

  include_context 'rake'

  it 'has a db:reset prerequisite' do
    expect(subject.prerequisites).to include('db:reset')
  end