Testing Rake Tasks in Rails
Article Table of Contents
I recently wrote a rake task to update some values we’ve got stored in the database. The rake task itself isn’t important in this post, but testing it is.
We’ve got many untested rake tasks in the database, so when our senior dev suggested adding a test, I had to build ours from scratch.
I did a bit more whack-a-moling with error messages than I’d hoped, so here’s a template of that test, along with some details that might save you some time, next time you are writing tests for your rake tasks.
We’re in a not-new version of Rails, and using Minitest. I’ve anonymized it. Hope it’s useful!
# test/tasks/rake_task_file_test.rb require 'test_helper' require 'rake' class RakeTaskFileTaskTest < ActiveSupport::TestCase describe 'namespace:task_name' do def setup @tt = Fabricate(:object_with_attributes_i_need_to_change) ApplicationName::Application.load_tasks if Rake::Task.tasks.empty? Rake::Task["namespace:task_name"].invoke end it "should change 'thing I don't want'" do @tt.reload values = @tt.attribute_i_changed refute_includes values, "thing I don't want" assert_includes values, "thing I do want" end end end
Notes on the above:
require 'rake'- I was getting a
NoMethodError: undefined method 'namespace' for main:Objectuntil adding this line. Found the answer in an unrelated-ish github issue, of course.
The rake task reads
@tt.attribute_i_changed, does logic on it, and then changes the value. The object I was changing had quite a few dependencies on other objects, so I just copied an existing factory, changed the values as needed, and called that factory in the
ApplicationName::Application.load_tasks if Rake::Task.tasks.empty?makes all the rake tasks available inside this test. Without
.load_tasks, nothing else works. Without
if Rake::Task.tasks.empty?makes sure it loads them only if they’re not currently loaded. (Thanks @Ratanachai Ken Sombat)
Rake::Task["namespace:task_name"].invokeruns the task under test.
@tt.reloadis very important. It’s obvious in hindsight, but since the rake task modified values of
@tt, I have to reload it from the database. Otherwise, the test has no idea the values changed when I call
And a few standard
assert_includes, and we’re on our way.