We'll see that every partial mock is a wasted opportunity: instead of dropping a spy in there, think a bit about redesigning the system on finer-grained level of abstractions. Instead of mocking a method in your class, think of extracting it away in another class instead, and use a 'regular' mock. These are the slides from my quickie session at Devoxx Poland 2017: https://youtu.be/pYG0jhCfT2A

1. victor.rentea@gmail.com www.VictorRentea.ro @victorrentea#DevoxxPL
Platinum Sponsor:
A Tale About The Evil Partial Mock,
And the Separation by Layers of Abstraction
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Spring, JavaEE, Hibernate
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Victor Rentea
Consultant, Technical Lead
Lead Architect for major IBM client
2
Independent Trainer
Clean Code Evangelist
victor.rentea@gmail.com VictorRentea.ro@victorrentea
1000+ devs. 1500+ hrs. 5 yrs.

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Rules of Simple Design
3
- Kent Beck
https://martinfowler.com/bliki/BeckDesignRules.html
2. Reveals Intention
3. No Duplication
4. Fewest Elements
1. Passes the Tests

4. VictorRentea.ro4
“Do TDD!
1. Passes the Tests

5. VictorRentea.ro
Rules of Simple Design
5 https://martinfowler.com/bliki/BeckDesignRules.html
2. Reveals Intention
3. No Duplication
4. Fewest Elements
1. Passes the Tests

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“Write Expressive Code
 Go to The Art of Clean Code Talk
(today at 1630, Room 1)
2. Reveals Intention

7. VictorRentea.ro
Rules of Simple Design
7 https://martinfowler.com/bliki/BeckDesignRules.html
2. Reveals Intention
3. No Duplication
4. Fewest Elements
1. Passes the Tests

8. VictorRentea.ro
DIE
8
3. No Duplication

9. VictorRentea.ro
DRY
9
Duplication Is Evil
3. No Duplication
D I E

10. VictorRentea.ro
SPOT
10
Don’t Repeat Yourself
Duplication Is Evil
3. No Duplication
D R Y

11. VictorRentea.ro11
Don’t Repeat Yourself
Duplication Is Evil
Single Point Of Truth
3. No Duplication
D R Y
S P O T

12. VictorRentea.ro
Rules of Simple Design
12 https://martinfowler.com/bliki/BeckDesignRules.html
2. Reveals Intention
3. No Duplication
4. Fewest Elements
1. Passes the Tests

13. VictorRentea.ro13
Premature Overengineering
4. Fewest Elements
Premature Optimization
FEAR
of new functionalities
of not meeting the NFR
Let’s write code, more code....

14. VictorRentea.ro
Rules of Simple Design
14 https://martinfowler.com/bliki/BeckDesignRules.html
2. Reveals Intention
3. No Duplication
4. Fewest Elements
1. Passes the Tests

15. VictorRentea.ro
Ordering the
Rules of Simple Design
15
Reveals Intention
No Duplication
Fewest Elements
Passes the Tests

16. VictorRentea.ro
Ordering the
Rules of Simple Design
16
Reveals Intention
No Duplication
Fewest Elements

17. VictorRentea.ro
Ordering the
Rules of Simple Design
17
Reveals Intention
No Duplication
Fewest Elements

18. VictorRentea.ro
Ordering the
Rules of Simple Design
18
Reveals Intention Fewest ElementsVS
CustomerFacade
saveCustomer()
getCustomer()
searchCustomer()
saveCustomerPreferences()
getCustomerPreferences()
validateAddress()
resetPassword()
checkPassworStrength()
CustomerPreferecesFacade
saveCustomerPreferences()
getCustomerPreferences()
validateAddress()
resetPassword()
checkPassworStrength()
CustomerFacade
saveCustomer()
getCustomer()
searchCustomer()
Same level of abstraction
Huh?

19. VictorRentea.ro
Ordering the
Rules of Simple Design
19
Reveals Intention
No Duplication
Fewest Elements

20. VictorRentea.ro
Ordering the
Rules of Simple Design
20
No Duplication Fewest ElementsVS
OrderService
AlertService
DeliveryService
Different level of abstraction
Extract for Reuse
sendEmail()
Wat!?
Super-funny IT clip:
https://www.destroyallsoftware.com/talks/wat

21. @
VictorRentea.ro
In L/XL apps: hard to detect reuse opportunities
 Pair Programming, design brainstorming
21
Extract for Reuse
Increase the Bus Factor

22. @
VictorRentea.ro22
But what about The First Rule?

23. @
VictorRentea.ro23
One for All,
All for One
tests production

24. VictorRentea.ro24
OrderService
EmailService
PARTIAL MOCK
(normal)MOCK
private sendEmail() public sendEmail()
Separation by Layers of Abstraction
A Tale about Test Overlapping and the Evil Partial Mock...
DrivenbyTests
Refactor tests
using mocks
Which methods
are more abstract ?Don’t do that !!
Partial Mocks are Evil !
Oh!.. Why?
Dunno..
Overlaping
Tests !!
public placeOrder()
public shipOrder()
a.k.a. “spy”

25. VictorRentea.ro25

26. VictorRentea.ro26
A Tale about Test Overlapping and the Evil Partial Mock...
Morale
Tempted to use a Partial Mock
to reduce Test Overlapping ?
Try to Separate By Layers of Abstraction
Simple, better factored code/tests

27. VictorRentea.ro
Rules of Simple Design
27 https://martinfowler.com/bliki/BeckDesignRules.html
2. Reveals Intention
3. No Duplication
4. Fewest Elements
1. Passes the Tests

28. victor.rentea@gmail.com www.VictorRentea.ro @victorrentea#DevoxxPL
Platinum Sponsor:
A Tale About The Evil Partial Mock,
And the Separation by Layers of Abstraction
Victor Rentea

29. victor.rentea@gmail.com www.VictorRentea.ro @victorrentea#DevoxxPL
Platinum Sponsor:
A Tale About The Evil Partial Mock,
And the Separation by Layers of Abstraction
Victor Rentea
Expressive Code
The Art of Clean Code
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