Testing Rake Tasks

A talk on how and why to test Rake tasks given at Test Ruby PDX in March 2016. See more details at: http://bit.ly/testing-rake-tasks

1. Testing Rake Tasks Brett Chalupa Test Ruby PDX March 2016 1
2. Hi, my name is Brett. I develop software for a non-profit called charity: water. 2
3. About Brett • Programming for 10 years • Using Ruby for the past 5 years • TDD-ing for the past 3 years • Primarily using RSpec, but MiniTest 3
4. Talk Overview • Rake explained • Why test Rake tasks • How to test Rake tasks • Rails-specific examples • Live coding TDD flow 4
5. Rake Explained 5
6. –Martin Fowler “Rake is a build language, similar in purpose to make and ant.” 6 http://martinfowler.com/articles/rake.html
7. 7 Rake is a tool for writing and executing tasks with Ruby and a custom DSL.
8. 8 Rake tasks can depend upon and call other Rake tasks.
9. Some Use Cases • Compiling an application (rake compile ) • Deploying a web app (rake deploy ) • Running an entire test suite (rake test:all ) • Data migrations (rake data_migrations:split_full_names ) • Running recurring tasks (Heroku Scheduler) 9
10. Rails Uses Rake • Managing the database (rake db:create, rake db:migrate ) • Outputting code stats (rake stats ) • Viewing routes (rake routes ) • Checking app details (rake about ) • So much more (run rake -T to see all tasks for a project) 10
11. A Simple Rake Task 11 desc 'Outputs a greeting to stdout' task :hello do puts 'Hello!' end $ rake -T rake hello # Outputs a greeting to stdout $ rake hello Hello! Output Rakefile
12. Why Test Rake Tasks 12
13. 13 For the first few years of using Ruby, I did not test Rake tasks.
14. 14 I was not even sure how to test Rake tasks.
15. 15 When writing Rake tasks, I had to abandon TDD.
16. 16 Ensuring Rake tasks worked became a matter of instead of .
17. 17 I kept wondering, “what makes Rake tasks different than any other code?”
18. 18 I started testing Rake tasks, and it has led to more confidence in creating and changing them.
19. 19 The reasons for testing Rake tasks are the same for testing any code.
20. How to Test Rake Tasks 20
21. 21 Since Rake uses Ruby, the approach for testing tasks is similar to testing Ruby code.
22. 22 Here is what the test for the hello task from earlier could look like.
23. Hello Task (Again) 23 desc 'Outputs a greeting to stdout' task :hello do puts 'Hello!' end $ rake -T rake hello # Outputs a greeting to stdout $ rake hello Hello! Output Rakefile
24. 24 require ‘rake' load ‘Rakefile’ describe ‘Rake tasks' do describe 'hello' do it 'outputs Hello! to stdout' do expect do Rake::Task['hello'].invoke end.to output("Hello!\n").to_stdout end end end
25. Two Kinds of Tests • Feature level - what is the expected outcome of the task being run? • Unit level - what code is being called from the task? 25
26. Feature Test Examples • Data changes • Output to stdout • Operating system changes (file, processes, etc.) 26
27. Unit Test Examples • Worker being queued • Object instantiation and method calls 27
28. 28 Sometimes both feature and unit tests do not make sense for Rake tasks.
29. 29 The hello test is a feature level spec.
30. 30 hello is so simple, is a unit test needed?
31. 31 Let’s tweak the hello task a little.
32. 32 class Greeter def greet puts 'Hello!' end end
33. 33 require_relative 'greeter' desc 'Outputs a greeting to stdout' task :hello do Greeter.new.greet end
34. 34 Now Greeter is responsible for greeting, which can be unit tested.
35. 35 require ‘rake' require_relative ‘greeter' load ‘Rakefile’ describe 'Rakefile units' do describe 'hello' do it 'uses a Greeter to greet' do expect(Greeter).to receive_message_chain( :new, :greet ) Rake::Task['hello'].invoke end end end
36. 36 describe 'hello' do it 'uses a Greeter to greet' do expect(Greeter).to receive_message_chain( :new, :greet ) Rake::Task['hello'].invoke end end
37. 37 The unit test covers the implementation of the Rake task. The feature test covers the expected outcome of the Rake task.
38. 38 This example is a bit trivial, but it lays the groundwork for how to test more complex Rake tasks.
39. 39 Here are some smaller bits of info to know when testing Rake tasks.
40. 40 Use the #load method to make different Rake tasks available. # at the top of the spec require ‘rake’ load ‘some_other_file.rake’
41. 41 Use Rake::Task[‘task_name’].reenable to allow the Rake task to be invoked again. Rake::Task['hello'].invoke Rake::Task['hello'].reenable Rake::Task['hello'].invoke
42. Testing Rake Tasks in Rails Apps 42
43. 43 Here is what it would look like to unit test an async ActiveJob job being queued.
44. 44 require 'rails_helper' describe 'donors sync' do describe 'donors:sync_modified_between' do subject { Rake::Task['donors:sync_modified_between'] } before { subject.reenable } it 'triggers the sync job for the donors' do expect(DonorsSyncJob).to receive( :perform_later ).with('2015-09-17', '2015-09-18') subject.invoke('2015-09-17', '2015-09-18') end end end
45. 45 it 'triggers the sync job for the donors' do expect(DonorsSyncJob).to receive( :perform_later ).with('2015-09-17', '2015-09-18') subject.invoke('2015-09-17', '2015-09-18') end
46. 46 namespace :donors do desc 'Sync donors' task :sync_modified_between, [:start_at, :end_at] => [:environment] do |_t, args| DonorsSyncJob.perform_later( args[:start_at], args[:end_at] ) end end
47. 47 In Rails apps, Rake tasks live in the lib/tasks directory.
48. 48 Add Rails.application.load_tasks to the spec/rails_helper.rb to load the Rake tasks.
49. 49 There are not much differences with Rails vs. plain old Ruby when testing Rake tasks. There is no need to explicitly load the Rake files, which is nice.
50. Live coding! 50
51. 51 The slides and code can be viewed here: http://bit.ly/testing-rake-tasks
52. Any questions? 52
53. Thank you! 53