How to test model's callback method independently? - ruby-on-rails

Question

I had a method in a model:
class Article < ActiveRecord::Base
def do_something
end
end
I also had a unit test for this method:
# spec/models/article_spec.rb
describe "#do_something" do
#article = FactoryGirl.create(:article)
it "should work as expected" do
#article.do_something
expect(#article).to have_something
end
# ...several other examples for different cases
end
Everything was fine until I found it's better to move this method into a after_save callback:
class Article < ActiveRecord::Base
after_save :do_something
def do_something
end
end
Now all my tests about this method broken. I have to fix it by:
No more specific call to do_something because create or save will trigger this method as well, or I'll meet duplicate db actions.
Change create to build
Test respond_to
Use general model.save instead of individual method call model.do_something
describe "#do_something" do
#article = FactoryGirl.build(:article)
it "should work as expected" do
expect{#article.save}.not_to raise_error
expect(#article).to have_something
expect(#article).to respond_to(:do_something)
end
end
The test passed but my concern is it's no longer about the specific method. The effect will be mixed with other callbacks if more added.
My question is, is there any beautiful way to test model's instance methods independently that becoming a callback?

Answer 1

Callback and Callback behavior are independent tests. If you want to check an after_save callback, you need to think of it as two things:
Is the callback being fired for the right events?
Is the called function doing the right thing?
Assume you have the Article class with many callbacks, this is how you would test:
class Article < ActiveRecord::Base
after_save :do_something
after_destroy :do_something_else
...
end
it "triggers do_something on save" do
expect(#article).to receive(:do_something)
#article.save
end
it "triggers do_something_else on destroy" do
expect(#article).to receive(:do_something_else)
#article.destroy
end
it "#do_something should work as expected" do
# Actual tests for do_something method
end
This decouples your callbacks from behavior. For example, you could trigger the same callback method article.do_something when some other related object is updated, say like user.before_save { user.article.do_something }. This will accomodate all those.
So, keep testing your methods as usual. Worry about the callbacks separately.
Edit: typos and potential misconceptions
Edit: change "do something" to "trigger something"

Answer 2

You can use shoulda-callback-matchers to test existence of your callbacks without calling them.
describe Article do
it { is_expected.to callback(:do_something).after(:save) }
end
If you also want to test the behaviour of the callback:
describe Article do
...
describe "#do_something" do
it "gives the article something" do
#article.save
expect(#article).to have_something
end
end
end

Answer 3

I like to use ActiveRecord #run_callbacks method to make sure callbacks are been called without need to hit database. This way it runs faster.
describe "#save" do
let(:article) { FactoryBot.build(:article) }
it "runs .do_something after save" do
expect(article).to receive(:do_something)
article.run_callbacks(:save)
end
end
And to test the behavior of #do_something you add another test specifically for that.
describe "#do_something" do
let(:article) { FactoryBot.build(:article) }
it "return thing" do
expect(article.do_something).to be_eq("thing")
end
end

Answer 4

In the spirit of Sandi Metz and minimalist testing, the suggestion in https://stackoverflow.com/a/16678194/2001785 to confirm the call to a possibly private method does not seem right to me.
Testing a publicly-observable side-effect or confirming an outgoing command message makes more sense to me. Christian Rolle provided an example at http://www.chrisrolle.com/en/blog/activerecord-callback-tests-with-rspec.

Answer 5

This is more of a comment than an answer, but I put it here for the syntax highlighting...
I wanted a way to skip the callbacks in my tests, this is what I did. (This might help with the tests that broke.)
class Article < ActiveRecord::Base
attr_accessor :save_without_callbacks
after_save :do_something
def do_something_in_db
unless self.save_without_callbacks
# do something here
end
end
end
# spec/models/article_spec.rb
describe Article do
context "after_save callback" do
[true,false].each do |save_without_callbacks|
context "with#{save_without_callbacks ? 'out' : nil} callbacks" do
let(:article) do
a = FactoryGirl.build(:article)
a.save_without_callbacks = save_without_callbacks
end
it do
if save_without_callbacks
# do something in db
else
# don't do something in db
end
end
end
end
end
end

Answer 6

describe "#do_something" do
it "gives the article something" do
#article = FactoryGirl.build(:article)
expect(#article).to have_something
#article.save
end
end