Safe Testing in Ruby

“Safe testing”
@sebasporto
Thursday, 26 September 13

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

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Things get complicated
user
language
location
roles
permissions

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

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Problem 1:
A whole universe to test
one thing

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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

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SLOW!!!

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Doubles! Stubs!

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class User
def watch(video)
...
end
end
Much faster!!
No interaction
with video
anymore
let(:video) { double.as_null_object }
it {
user.watch(video)
}

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it {
user.watch(video)
}
But it may break
class User
def watch(video)
...
end
end
class Video
def seen_by(user)
...
end
end
Test still passes!

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Not to worry.
Integration test
will save you!

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Integration breaks
Fix the code in B
Unit test for B breaks
Fix unit test for B
Change code in A

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Integration test coverage?
Will they?

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Your test

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Your app

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Can we get beneﬁts
without the drawbacks?

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Safer testing
Rspec ﬁre
Quacky
Bogus
...

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Bogus
Safe Fakes
Safe Stubbing
Safe Mocks

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Fakes

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class User
def watch(video)
...
end
end
Rspec doubles
it {
user.watch(video)
...
1 example, 0 failures still passes
class Video
def seen_by(user)
...
end
end

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class User
def watch(video)
...
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)
...

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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
it {
user.watch(video)
...

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Stubbing

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Rspec Stubbing
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

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Bogus Stubbing
before do
stub(video)
.time{ 14.minutes }
end
it {
user.watch(video)
}
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

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Stubbing (args)
wrong number of arguments (0 for 1)
before do
stub(video)
.time(any_args){ 14.minutes }
end
it {
user.watch(video)
}
class User
...
def busy_for
current_video.time
end
...
end
class Video
def time(args)
...
end

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Expectations
(Mocking)

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Rspec Mocking
it {
video.stub(:watched_by)
user.watch(video)
expect(video).to
have_received(watched_by)
}
1 example, 0 failures
class User
...
def watch(video)
...
end
...
class Video
def seen_by(person)
...
end
end

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Bogus Mocks
it {
mock(video).watched_by(any_args)
user.watch(video)
}
does not respond to watched_by
class User
...
def watch(video)
...
end
...
class Video
def seen_by(person)
...
end
end

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Bogus gem
https://www.relishapp.com/bogus

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Thanks
@sebasporto

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Safe Testing in Ruby

Safe Testing in Ruby

sporto

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