intro to mocking - djangocon 2015
TRANSCRIPT
Intro To Mocking:
Why Unit Testing Doesn’t Have to Be So Hard!
Daniel Davis
@Ooblioob
• Software Developer for 8 years
• Senior Consultant: Excella Consulting in
Washington, DC
• Fun Fact:
– I ran the “Jingle All The Way” 5k dressed as a
Giant Gingerbread man
A Little About Me…
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Survey Time!
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• Struggled with unit testing until I learned
about Mocking
Learning To Test
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Me Learning about Mocking…
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Image credit: http://stylecaster.com/excited-gif/
Many of us are in the same boat…
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• “I wish someone would just give a talk on
this…”
• So if that’s you…
We all want to write better tests…
Let’s Talk About Unit Tests…
Unit – 70%
Integration
– 20%
UI
10%
Testing Types
• “They’re good when the problem is easy”
– A rabbit hole of testing
• “I spend too much time writing lots of code
to test, so I give up”
• “There’s just some stuff you can’t unit test”
Great Unit Testing Myths
Mocking makes unit testing easier!
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What Are Mocks?
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Test Double
Dummy
ObjectTest Stub Test Spy
Mock
Object
Fake
Object
Commonly referred to as “Mocks”
• Stubs
– Provide a canned response to method calls
• Spy
– Real objects that behave like normal except
when a specific condition is met
• Mocks
– Verifies behavior (calls) to a method
What Are Mocks?
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Blah Blah Blah professor Dan…
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• Eliminates dependencies
– Isolated Unit Tests
Problems Mocks Solve
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foo(x) bar(x)
• Tests methods that have no return value
Problems Mocks Solve
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How do we know that bar(x) has been called?
• Tests error handling
Problems Mocks Solve
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• Eliminate dependency on database calls
– Speed up testing!
• Reduce test complexity
– Don’t have to write complex logic to handle
behavior of methods not under test
• Don’t have to wait to implement other
methods
Other Reasons Mocks Are Important
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Ok, I’m sold…Show me how to actually do this…
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• Mock (MagicMock)– Most robust, popular
– Built-in as of Python 3.3!
• flexmock– Based on Ruby’s flexmock
• mox– Similar to Java’s EasyMock
• Mocker
• dingus– “record then assert” mocking library
• fudge– Similar to Mockito
• MiniMock– Simple mocking with DocTest
What Are The Python Options?
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Sample Problem
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Problem: Tinder Competitor
True love is an isolated
container…Image Credits:
- http://www.forbes.com/sites/jjcolao/2013/04/08/tinder-for-business-dating-app-looks-to-conquer-other-matchmaking-verticals/
- https://blog.docker.com
• Create a method to return a new, random
victim candidate
– Must not show the same person
– Must not show someone the user has already
“swiped” on
Problem: “Docker” dating app
Easy enough…
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“Surely no one could
have seen EVERYONE
in the database!!!”
- The Internget_next_person() get_random_person()
Write a Unit Test…
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It works!!!
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Noooooooooo!!!!
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Easy enough…
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What if knew the result of get_random_person()???
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PatchingModule.attribute
Mock method
It works EVERY SINGLE TIME!!!
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Variations on a theme
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Variations on a theme
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Variations on a theme
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Variations on a theme
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OMG, ContextManagers! WHAT???
But what if we call it multiple times???
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• What if I want to test the while loop?
Different results on multiple calls
Uh…umm…
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UMM…
Use side_effect
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• Use patching / mocks to bring certainty to
method calls
• Eliminates dependencies on other code
– Even unfinished code!!!
• Lots of ways to do it, pick your favorite
Recap: What did we learn?
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Mocking to Verify Behavior
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Problem: Matching in “Docker”
• When a user swipes right…
• If the other user “likes” them:
– Send them both a message with contact info
• If the other user “dislikes” them:
– Let the user down gently…
• If the other user hasn’t evaluated yet:
– Display the “give it time” message
Problem: “Docker” matches
Implementation
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How do we test this??? No return values!!!
Behavior Verification
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What about checking parameters???
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Verifying Parameters
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Shouldn’t we check the other
methods too?
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We’d need to have multiple mocks to do that!!!
Multiple Mocks
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Patch Multiple
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Testing Multiple Calls…
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Multiple calls
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Whew!!!Almost Done!The day is almost over!
You can sleep later!
Image Credits:
- http://www.clickhole.com/article/8-kittens-god-forbid-could-be-used-prop-wobbly-tab-1364
- http://stuffpoint.com/dogs/image/208632/adorable-corgi-puppies-running-ddddd-picture/
Mocking Exceptions
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Sample Problem: Docker Payments with Stripe
Stripe Payment Code
Stripe Testing…ugh!
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• Requires us to call the API
• Unclear what those numbers mean
• Must create the stripe_token
– Not a dictionary of CC fields
– Encrypted
That’s ridiculous…
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There’s got to be a better way…
…have you tried Mocking???
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Mocking an Exception
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Wrap Up:Key Take-Aways
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• Mocking makes writing unit tests simpler
– Eliminates dependencies
– Verifies behavior
– Tests error handling
• You just need some practice!
Remember This!
• http://mock.readthedocs.org/en/latest/
• Pip Install Mock (Python 2)
• Create a simple class, then write tests!
Try It On Your Own
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Let’s Go Write Some Tests!!!
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