Testing Rake Tasks

I’ve worked in several teams that used (and still use) Rake, a build tool written in Ruby, to perform various tasks—not just building software (or other artefacts). In this article I list some ways in which rake tasks can be tested, but I do not recommend all of them for all contexts.

Ways to test rake tasks

1. You don’t

Let’s face it, in some cases rake tasks are hardly tested at all, maybe just tried out a little bit. And in fact in some cases that’s just fine: When the tasks are particularly simple and/or they’re short lived anyway, a whole set of tests may be just too much. — But keep in mind that in this case using rake may also be going too far already.

For example, take to following code.

desc 'Write list of files in (sub) folders to "filelist.txt"'
task :dir_to_txt do
  File.open('filelist.txt', 'w') do | f |
    f.puts Dir['**/*']
  end
end

For most people this code is so simple, that they likely wouldn't bother testing it (and yet… I'm not claiming it's bug-free).

2. Non-Automated Testing

In many cases, rake tasks are 'tested' by manually running them and then examining the result. Depending on what you're doing this can be fine. However, rake tasks process various input and they can be configured, too. For example, you may set an environment (such as 'test', 'development, 'production') or a particular server to run them against. Sometimes you can cover the important combinations with manual testing. But then, maybe you're missing a particular combination that causes a failure.

Also, don't forget to document what, how and why you tested it the way you did. Someday someone will have to change the rake task, and then it will be important to know what behaviour is expected not to change.

2. Cucumber

You're running the rake tasks in order to have a (more or less) permanent effect. You can test this using Cucumber, and the format could be like this:

Feature: Running task name_space:task_name
Scenario: Use default parameters
  Given the task is configured with the following setup
    | parameter_1 | 'some value' |
    | parameter_2 | a_number |
  When rake name_space:task_name is run
  Then some effect should be achieved

With Cucumber you can provide configuration data to run a single setup like the one above, but Cucumber also offers 'Scenario Outlines' which provide an even more parameterised way to run the checks. Combined with e.g. 'all pairs testing', this can give a very reasonable test coverage (with respect to used values & combinations of these values).

3. MiniTest or RSpec + Refactored Rake Tasks

A rake task is just Ruby code. Therefore it can be unit tested just like any other Ruby code. (It can even be developed in a test-first way. Just saying.) If you're also refactoring tasks into modules, classes and methods, it's even easier to test and an additional benefit may be the fact that you're creating an interface to the tasks that may be useful in a context other then running rake tasks.

4. 'Redefine' Rake Methods

Rake tasks are called using:

rake a_taskname

Rake searches for a file called 'Rakefile' (or 'rakefile', with or without the '.rb' suffix), and then processes it, in order to find a task with a matching name. Since the Rakefile itself doesn't require 'rake' (using the command rake loads Rake's context), you can (re-) define the methods rake provides (in a separate file), require that file, require your Rakefile and then use a test framework of your choice on those methods. Let's look at a Rakefile with two simple tasks:

require 'fileutils'
namespace :doc do
  desc "Generate RDoc for the Rakefile"
  task :self do
    `rdoc ./Rakefile`
  end

  desc "Remove doc folder and its content"
  task :remove do
      FileUtils.rm_rf('doc')
    end
  end
end

While you could (re-) define rake's methods 'namespace', 'desc', 'task' etc. and the call those methods to test them, this would only solve part of the problem: The tasks still change the outside world (in this case generate RDoc in a folder in one case and remove that fold in the other case). In at least some cases that's undesirable, e.g. when there's a task that's supposed to switch your online shop into maintenance mode, just displaying a static page for all incoming requests. At least in those cases it's preferable to check for the right behaviour instead of depending on checking a state change in the (real) world.

That's possible in Ruby: You can redefine existing methods such as FileUtils.rm_rf and even ` in the example above. — Yes ` (the back tick) is a method in Ruby and you can redefine it. For more complicated (or complex) rake tasks, it's a lot of work to find all the methods that you'd need to redefine. While it's possible, I wouldn't recommend it, since it seems to me that it's also error prone and might well introduce more trouble (read: bugs) than anyone would like in their tests.

Some General Remarks

Since a rake task is code, I think it should be treated as carefully as any other code we write and it should be tested (and live in the same version control system used for other parts of the code base). Especially in case of tasks that control an online shop (e.g. switch to maintenance mode), deploy new software to production etc. it is in fact production code.

I personally prefer the rake tasks I'm working with to be well written, refactored and of course tested code. So I strive to extract single methods, modules and classes from rake tasks and test these in isolation.

Not matter what kind of automation you're using to test your rake tasks, as soon as you're starting to use a rake task to run these tests, e.g. as part of your regression tests on a Continuous Integration system like Jenkins, things may get tangled up: How would you test those rake tasks?

Other Articles on Testing Rake Tasks

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1 Comment

  1. Testing Bits – 12/22/13-12/28/13 | Testing Curator Blog

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