Write Better Tests
With Mock!
If You're Not Writing Unit Tests Today
Shame On You!
If You're Not Writing Unit Tests Tomorrow
Shame On Me!
About Me
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Python/DevOps developer by day
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Django District organizer by night
New (To Me) In 2016:
"Continuous attention to technical excellence
and good design enhances agility."
Martin Fowler's Testing Pyramid
Reasons to Write Unit Tests
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Martin Fowler said so
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Prove to myself that the code works
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Alert me if something breaks in the future
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Comfortably make future changes
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A gift to future developers
I'm not writing unit tests because _____
Common Excuses For Not Writing Tests
it's hard / intimidating
it takes too long
it doesn't benefit me
my code is always perfect
failing tests + CI = embarrassment
The Itinerary
1) Discuss common scenarios that make writing tests difficult
The Itinerary
2) Show how we can use "mocking" to simplify writing the tests
The Itinerary
3) We all walk out the door feeling confident about writing tests
What the heck is mocking?!?
Tease or laugh at in a scornful or contemptuous manner
Another definition of 'mock':
Not authentic or real, but without the intention to deceive
Mocking is the practice of replacing an object in your code with a fake object for the purpose of executing a test
In software development:
For a fun read on the nuances of:
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Mock
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Test Double
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Stub
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Fake
search google for "The Little Mocker"
Mocking in Python
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'mock' library is the most popular
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'pip install mock' in python 2
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built into python 3
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Well documented... but not straight forward
Let's get some sample code!
Mike, don't forget...
Github README
requirements.txt
Web app
Exercise 1:
Mocking Bird
Exercise 1: Mocking Bird
The tests actually pass... sometimes...
Let's run the tests 10 times:
for i in {1..10}; do
pytest tests/test_mocking_bird.py
done | grep secondsWhat Can Mock Do For You?
Create predictable scenarios for interfaces that have unpredictable results
Exercise 1: Mocking Bird
Mock tools required:
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patch
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return_value
Exercise 1: Mocking Bird
Exercise 2:
Mocking Me
Exercise 2: Mocking Me
The code for via_gif hits an external API.
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How do we test that the function handles response codes correctly?
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Do the tests run quickly?
What Can Mock Do For You?
Run tests even if the API is not available
Test the rare edge cases
Tests run quickly even if the real interface is slow
Exercise 2: Mocking Me
Mocking is a mechanism to decouple outside dependencies, enabling the testing of an individual unit of code.
A Better Definition of 'mock'
Mock tools required:
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patch
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return_value
Exercise 2: Mocking Me
Exercise 3:
Mocking Jay
Exercise 3: Mocking Jay
How do we test if hug() gets called when we expect it to?
What Can Mock Do For You?
Test interactions with interfaces that have no return value
Exercise 3: Mocking Jay
Mock tools required:
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patch
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called
Exercise 3: Mocking Jay
You're Now A Mocking Expert!
My One Takeaway:
Don't be intimidated by mocking, it makes writing tests easier!
Practice creates confidence
Questions?
mocking-guide-in-python
By m3brown
