Fake your test away: How to abuse your test doubles

@jenny_codes Fake your test away How to abuse your test
doubles

@jenny_codes

@jenny_codes @ RubyConf Taiwan 2019

@jenny_codes Let’s talk about Douglas Adams

@jenny_codes Let’s talk about Douglas Adams source: https://www.wallpaper fl are.com/don-t-panic-text-decor-the-hitchhiker-s-guide-to-the-galaxy-wallpaper-pwpgv

@jenny_codes Let’s talk about Douglas Adams Three stages in human
civilization: • Survival • Inquiry • Sophistication

civilization: • Survival: How? • Inquiry: Why? • Sophistication: Where?

civilization: • Survival: How can we eat? • Inquiry: Why? • Sophistication: Where?

civilization: • Survival: How can we eat? • Inquiry: Why do we eat? • Sophistication: Where?

civilization: • Survival: How can we eat? • Inquiry: Why do we eat? • Sophistication: Where shall we have lunch?

@jenny_codes Let’s talk about testing

@jenny_codes Three stages in my relationship with test doubles: Let’s
talk about testing

@jenny_codes Three stages in my relationship with test doubles •
Survival: How to use test doubles? Let’s talk about testing

Survival: How to use test doubles? • Inquiry: Why do I test? Let’s talk about testing

Survival: How to use test doubles? • Inquiry: Why do I test? • Sophistication: Where shall I begin to delete my old tests? Let’s talk about testing

@jenny_codes Outline • Unit tests, integration tests, and those in
between • Integration-test wannabes • Helicopter unit tests • How to not abuse your test doubles?

@jenny_codes Test double

@jenny_codes Test double ├─ Stub ├─ Mock └─ Spy

@jenny_codes Subject

@jenny_codes Dependency

Imagine a perfect world

@jenny_codes Testing pyramid Unit tests Integration tests Acceptance tests

@jenny_codes Testing pyramid, reality edition Integration-test wannabes Helicopter unit tests
Scream tests 🤔 🤔 🤔 🤔

@jenny_codes Testing pyramid, reality edition Helicopter unit tests Scream tests
🤔 🤔 🤔 🤔 Integration-test wannabes

@jenny_codes A restaurant that serves French toast

@jenny_codes The test

@jenny_codes 🤔 The test

@jenny_codes

@jenny_codes 🔎

@jenny_codes 🔎 🚨

@jenny_codes

@jenny_codes ⛔

@jenny_codes

@jenny_codes Integration-test wannabes (n.) Tests with randomly inserted test doubles
because the real objects are too awkward to deal with.

@jenny_codes ❌ Random doubles == Random test failures Integration-test wannabes

@jenny_codes One month later…

@jenny_codes One month later… FAILED

@jenny_codes Therapeutic Refactoring by Katrina Owen, Cascadia Ruby Conf 2012

@jenny_codes

@jenny_codes when I don’t have to modify 100 random test
failures for it

@jenny_codes ❌ Random doubles == Random test failures ❌ Decreased
productivity Integration-test wannabes

Test doubles are contracts

@jenny_codes Restaurant Service: Cheese Panini

@jenny_codes

@jenny_codes Chef Waiter Restaurant Service The dependency graph Floor 🛸
🌝 🐢 Cupboard Fridge Bread Cheese class-level dependency instance-level dependency

@jenny_codes The dependency graph 🙈 🙈 Chef Waiter Restaurant Service
Cupboard Fridge Bread Cheese class-level dependency instance-level dependency test double 🙈 🙈 🙈

@jenny_codes The dependency graph 🙈 🙈 Chef Waiter Restaurant Service
class-level dependency instance-level dependency test double 🙈 🙈 🙈 🙈 🙈

@jenny_codes

@jenny_codes Helicopter unit tests (n.) Tests that try to control
every implementation detail in the subject.

@jenny_codes ❌ Fake empire The helicopter unit tests

@jenny_codes https://media.giphy.com/media/IguL9zRYV20X1QeKuV/giphy.gif Production Your CI The helicopter unit tests

@jenny_codes ❌ Fake empire ❌ Brittle tests The helicopter unit
tests

tests GUARANTEED

tests x N

@jenny_codes hard-to-use code == hard-to-write test easy-to-use code == easy-to-write
test

@jenny_codes Tests are the first consumer of your API

@jenny_codes https://twitter.com/dan_abramov/status/1456265490754510848/photo/1 Write an unit test that can’t catch errors
Write an integration test that has holes it

@jenny_codes • 🎁 • 🎁 • 🎁 How to not
abuse your test doubles?

@jenny_codes • Use the Principle of Least Knowledge • 🎁
• 🎁 How to not abuse your test doubles?

@jenny_codes Principle of Least Knowledge Don’t talk to strangers

@jenny_codes Principle of Least Knowledge

@jenny_codes Principle of Least Knowledge Life Universe Everything Answer

@jenny_codes Principle of Least Knowledge Life Universe Answer Everything

@jenny_codes Principle of Least Knowledge Answer Everything Universe Life

@jenny_codes Principle of Least Knowledge Don’t talk to strangers Low
coupling

@jenny_codes

@jenny_codes Use Principle of Least Knowledge: Result

@jenny_codes • Use the Principle of Least Knowledge • 🎁
• 🎁 How to not abuse your test doubles?

@jenny_codes How to not abuse your test doubles? • Use
the Principle of Least Knowledge • Separate decisions and delegations. • 🎁

@jenny_codes Decision • Logic • Condition • Calculation • Dependency
• Relationships Delegation

@jenny_codes

@jenny_codes = delegation = decision

@jenny_codes 1. Get resources 2. Prepare ingredients 3. Make dish
4. Serve dish

@jenny_codes 1. Get resources

4. Serve dish

4. Serve dish => waiter => waiter => chef

@jenny_codes Separate decision and delegation: Result

@jenny_codes

@jenny_codes Separate decision and delegation: Result Arrange Act Assert

@jenny_codes Separate decision and delegation: Result

@jenny_codes Decision • Logic • Condition • Calculation • Unit
test • Dependency • Relationships Delegation

@jenny_codes Decision • Logic • Condition • Calculation • Unit
test • Dependency • Relationships • Integration test Delegation

@jenny_codes Testing pyramid with decision and delegation Unit tests Integration
tests Acceptance tests Decisions Delegation

@jenny_codes How to not abuse your test doubles? • Use
the Principle of Least Knowledge • Separate decisions and delegations • 🎁

@jenny_codes • Use the Principle of Least Knowledge • Separate
decision and delegation • Make the dependencies really obvious How to not abuse your test doubles?

@jenny_codes All dependencies are equal, but some are more equal
than others.

than others. the side-e ff ect free the rest

than others. the side-e ff ect free the rest 🤤

than others. the side-e ff ect free the rest 🤤 ⚠

@jenny_codes the side-e ff ect free 🤤 All dependencies are
equal, but some are more equal than others. the rest ⚠ ⚠ ⚠ ⚠ ⚠ ⚠⚠⚠ ⚠

@jenny_codes Revisit serve_french_toast

@jenny_codes Chef Waiter Restaurant Service Floor 🛸 🌝 🐢 class-level
dependency instance-level dependency Revisit serve_french_toast

@jenny_codes Revisit serve_french_toast Chef Waiter Restaurant Service Floor 🛸 🌝
🐢 class-level dependency instance-level dependency

🐢 class-level dependency instance-level dependency How to make those dependencies obvious?

🐢 class-level dependency instance-level dependency

@jenny_codes Chef Waiter Restaurant Service Floor 🛸 🌝 🐢

@jenny_codes Chef Waiter Restaurant Service Floor 🛸 🌝 🔻 🐢
Restaurant Repo

@jenny_codes

@jenny_codes ⚠ ⚠ ⚠

@jenny_codes

@jenny_codes Make dependencies obvious: Result

@jenny_codes • Use the Principle of Least Knowledge • Separate
decision and delegation • Make the dependencies really obvious How to not abuse your test doubles?

@jenny_codes Design your system so there’s no room to abuse
your test doubles

One last thing

@jenny_codes Talks that inspire me • Gary Bernhardt: Boundaries •
Justin Searls: Please don’t mock me • Justin Searls: How to stop hating your test • Katrina Owen: Therapeutic refactoring • All the talks by Sandi Metz really

@jenny_codes Books that inspire me • The Art of Unit
Testing by Roy Osherove • Domain Modeling Made Functional by Scott Wlaschin • The Hitchhiker’s Guide to the Galaxy by Douglas Adams

@jenny_codes Talk to me! or just @jenny_codes

Fake your test away: How to abuse your test dou...

Fake your test away: How to abuse your test doubles

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