“Safe testing” @sebasporto Thursday, 26 September 13 

user let(:user) { User.new } it “tests something” do expect(user).to be_something end Thursday, 26 September 13 

Things get complicated user language location roles permissions Thursday, 26 September 13 

let(:location) { Location.new } ... let(:user) { User.new(location: location, language: language) } We can create things manually Or use factories let(:user) { build(:user) } Thursday, 26 September 13 

Problem 1: A whole universe to test one thing Thursday, 26 September 13 

it ‘increase the watch count’ { user.watch(video) expect(user.watch_count).to } Problem 2: Too much happening class User def watch(video) ... video.watched_by(self) end end class Video def watched_by(user) ... end end Thursday, 26 September 13 

SLOW!!! Thursday, 26 September 13 

Doubles! Stubs! Thursday, 26 September 13 

class User def watch(video) ... video.watched_by(self) end end Much faster!! No interaction with video anymore let(:video) { double.as_null_object } it { user.watch(video) expect(user.watch_count).to } Thursday, 26 September 13 

let(:video) { double.as_null_object } it { user.watch(video) expect(user.watch_count).to } But it may break class User def watch(video) ... video.watched_by(self) end end class Video def seen_by(user) ... end end Test still passes! Thursday, 26 September 13 

Not to worry. Integration test will save you! Thursday, 26 September 13 

Integration breaks Fix the code in B Unit test for B breaks Fix unit test for B Change code in A Thursday, 26 September 13 

Integration test coverage? Will they? Thursday, 26 September 13 

Your test Thursday, 26 September 13 

Your app Thursday, 26 September 13 

Can we get benefits without the drawbacks? Thursday, 26 September 13 

Safer testing Rspec fire Quacky Bogus ... Thursday, 26 September 13 

Bogus Safe Fakes Safe Stubbing Safe Mocks Thursday, 26 September 13 

Fakes Thursday, 26 September 13 

class User def watch(video) ... video.watched_by(self) end end Rspec doubles let(:video) { double.as_null_object } it { user.watch(video) ... 1 example, 0 failures still passes class Video def seen_by(user) ... end end Thursday, 26 September 13 

class User def watch(video) ... video.watched_by(self) end end undefined method `watched_by' it breaks Bogus Fakes class Video def seen_by(person) ... end end fake(:video) { Video } it { user.watch(video) ... Thursday, 26 September 13 

wrong number of arguments (2 for 1) it breaks Fakes (args) class User def watch(video) ... video.watched_by(self, args) end end class Video def watched_by(user) ... end end fake(:video) { Video } it { user.watch(video) ... Thursday, 26 September 13 

Stubbing Thursday, 26 September 13 

Rspec Stubbing let(:video) { double.as_null_object } before do video .stub(:time) .and_return(14.minutes) end it { user.watch(video) expect(user.busy_for).to eq(14.minutes) 1 example, 0 failures passes even if video.time doesn’t exist class User ... def busy_for current_video.time end ... end class Video def duration ... end Thursday, 26 September 13 

Bogus Stubbing fake(:video) { Video } before do stub(video) .time{ 14.minutes } end it { user.watch(video) expect(user.busy_for).to eq(14.minutes) } does not respond to time This is what we want class User ... def busy_for current_video.time end ... end class Video def duration ... end Thursday, 26 September 13 

Stubbing (args) wrong number of arguments (0 for 1) fake(:video) { Video } before do stub(video) .time(any_args){ 14.minutes } end it { user.watch(video) expect(user.busy_for).to eq(14.minutes) } class User ... def busy_for current_video.time end ... end class Video def time(args) ... end Thursday, 26 September 13 

Expectations (Mocking) Thursday, 26 September 13 

Rspec Mocking let(:video) { double.as_null_object } it { video.stub(:watched_by) user.watch(video) expect(video).to have_received(watched_by) } 1 example, 0 failures class User ... def watch(video) ... video.watched_by(self) end ... class Video def seen_by(person) ... end end Thursday, 26 September 13 

Bogus Mocks let(:video) { double.as_null_object } it { mock(video).watched_by(any_args) user.watch(video) } does not respond to watched_by class User ... def watch(video) ... video.watched_by(self) end ... class Video def seen_by(person) ... end end Thursday, 26 September 13 

Bogus gem https://www.relishapp.com/bogus Thursday, 26 September 13 

Thanks @sebasporto Thursday, 26 September 13