Safe Testing in Ruby

A look at safe doubles, stubs and mock with Rspec and Bogus

Transcript

1. “Safe testing” @sebasporto Thursday, 26 September 13
2. user let(:user) { User.new } it “tests something” do expect(user).to be_something end Thursday, 26 September 13
3. Things get complicated user language location roles permissions Thursday, 26 September 13
4. 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
5. Problem 1: A whole universe to test one thing Thursday, 26 September 13
6. 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
7. SLOW!!! Thursday, 26 September 13
8. Doubles! Stubs! Thursday, 26 September 13
9. 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
10. 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
11. Not to worry. Integration test will save you! Thursday, 26 September 13
12. 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
13. Integration test coverage? Will they? Thursday, 26 September 13
14. Your test Thursday, 26 September 13
15. Your app Thursday, 26 September 13
16. Can we get benefits without the drawbacks? Thursday, 26 September 13
17. Safer testing Rspec fire Quacky Bogus ... Thursday, 26 September 13
18. Bogus Safe Fakes Safe Stubbing Safe Mocks Thursday, 26 September 13
19. Fakes Thursday, 26 September 13
20. 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
21. 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
22. 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
23. Stubbing Thursday, 26 September 13
24. 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
25. 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) } <Video:0x8051f2cc> 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
26. 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
27. Expectations (Mocking) Thursday, 26 September 13
28. 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
29. Bogus Mocks let(:video) { double.as_null_object } it { mock(video).watched_by(any_args) user.watch(video) } <Video:0x8051f2cc> 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
30. Bogus gem https://www.relishapp.com/bogus Thursday, 26 September 13
31. Thanks @sebasporto Thursday, 26 September 13