如何测试Rake任务回调

Question

I create test code with rspec. I want to test callback is executed or not.
task main: [:callback] means run callback before main , doesn't it?

But my test failed. I looks like callback is not executed. Why?

require 'rails_helper'
require 'rake'

RSpec.describe 'Rake::Task' do
  before(:all) do
    @rake = Rake::Application.new
    Rake.application = @rake
    Rake.application.rake_require('rspec_before', ["#{Rails.root}/lib/tasks"])
  end

  subject { @rake['rspec_before:main'].execute }

  it "expects run callback before main task" do
    expect{ subject }.to output(/Hello, world/).to_stdout
  end
end

My Rake task is below.

namespace :rspec_before do
  task :callback do
    @greeting = "Hello, world"
  end

  # case 1
  # In this case, `callback` is NOT executed in rspec
  # In console, `callback` is executed !!!!
  desc "main task"
  task main: [:callback] do
    puts @greeting
  end

  # case 2
  # In this case, `callback` is executed in rspec
  # task :main do
  #   Rake::Task['rspec_before:callback'].execute
  #   puts @greeting
  # end
end

Answer 1

So, I'm not sure I would call :callback a callback , it's more of a dependency . A callback implies it happens after the main task is done, whereas when you do

task main: [:callback]

what you're really saying is that you depend on the other task having run first. So I would end up changing the name of that, though that's probably just a sample/throwaway name for this question. But, I digress and I'll continue calling the task :callback as written for this answer.

---

The main issue here is that when you call execute on a rake task, only that task gets executed. This is because there may be situations where you don't want or need to call the entire dependency chain. Let's say we add another task to your file:

desc "secondary task"
task :secondary do
  @greeting = 'Goodbye, Cruel World'

  Rake::Task['rspec_before:main'].execute
end

If we run this, we very likely want the main task to output Goodbye, Cruel World , instead of Hello, World and if we call all the dependencies, main would end up calling :callback which would override our @greeting and end up outputting Hello, World .

There is, however, another task that does call the entire dependency chain: invoke :

desc "secondary task"
task :secondary do
  @greeting = 'Goodbye, Cruel World'
  Rake::Task['rspec_before:main'].invoke
end

if we run this task, now we'll see Hello, World instead of Goodbye, Cruel World . So, having said all of this, what does that mean for your RSpec test? You simply need to change your subject to:

subject { @rake['rspec_before:main'].invoke }

because you are wanting to run the dependencies.