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Are Your Tests Slowing You Down?
Trisha Gee
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https://trishagee.com/books/
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Tests Make You More Productive?
Tests Make You More Productive
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So it’s OK not to write tests, right?
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“Testing is Xanax for programmers, it’s an anxiety
reducing technique.”
https://youtu.be/guycIP56YeY
Kent Beck
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What slows down your testing?
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What slows down your testing?
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What slows down your testing?
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1. Writing
2. Troubleshooting
3. Running
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1. Writing Tests Takes Time
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Use Your IDE
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AI Will Make You Super Productive
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AI is good for generating mundane and/or predictable code
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AI is good for generating test data
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AI can consider edge cases we haven’t thought of
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AI is a decent companion
…but it doesn’t replace you
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AI is a lying toad
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“The keyboard is not the bottleneck.”
Dave Farley
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“The productivity myth suggests that anything we
spend time on is up for automation…. The importance
and value of thinking about our work and why we do it
is waved away as a distraction. The goal of writing… is
filling a page rather than the process of thought that a
completed page represents.”
https://www.techpolicy.press/challenging-the-myths-of-generative-ai/
Eryk Salvaggio
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Bring a friend
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“We recommend that the developers, who are good at
writing efficient, maintainable code, work together
with the testers, who are good at specifying test cases,
to automate tests.”
Agile Testing Condensed: A Brief Introduction
Lisa Crispin, Janet Gregory
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https://bit.ly/3RG85vc
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“Creativity is a wild mind and a disciplined eye.”
Dorothy Parker
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Invest the time in writing to save time troubleshooting
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2. Troubleshooting Takes Time
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What is this test anyway?
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Your test needs to tell you what is expected and why,
so you understand what to do when it fails.
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Why do tests fail?
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‣ Code is wrong
‣ Test is wrong
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Something changed
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• Production code
• Test code
• Refactoring/structure
• Data
• Infrastructure
• Load or usage
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1. Whose fault is it?
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1. Triage
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• Production code
• Test code
• Refactoring/structure
• Data
• Infrastructure
• Load or usage
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You need data
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2. Fix it
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“Your best and wisest refuge from all troubles is in your
science.”
Ada Lovelace
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Data is key
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Tools for seeing more
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Automation is your friend
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Learn how to use your debugger!
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Aim for fast feedback and easy
reproduction
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“99.9% of the time the best way to troubleshoot a test
is to re-write it so it’s smaller and faster.”
Israel Boza Rodriguez (@IsraKaos)
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Fixed!
✅
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Let’s talk about “unreliable test results”
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I have made the decision to trust you
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1. Find Your Flaky Tests
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This is NOT a fix!
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So now you can ignore those flaky tests
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2. Quarantine your flaky tests
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3. Fix your flaky tests!!!
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If you add a new test and it’s flaky
Or are working on a test and it becomes flaky
Fix it now!!
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1. When they impact you directly
2. Attach them to related functionality
3. Flaky Test Days
4. Add flaky tests to the backlog
5. 20% time, tech debt time, cleanup time…
Make Time To Fix Flaky Tests
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1. Environment, Network, and Resources
2. Integration Points
3. Concurrency, Asynchronous Programming, and Waiting
4. Setup/Teardown and Test Data
5. System Behaviour
Causes of flakiness
Known good practices and tools
Not always in my control
Try to minimise these
Can be REALLY HARD
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https://youtu.be/vHBzZHE4tJ0
1. Environment
2. Test Data
3. Versioning
4. Resource Use
5. System Behaviour
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3. Running Tests Takes Time
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What slows down your testing?
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How do you speed up your tests?
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Use a Build Cache
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Very effective for multi-module projects
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No cache: Full build required
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Build cache: Changing a leaf module
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Build cache: Changing a module’s implementation
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Build cache: Changing core implementation
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Remote Build Cache
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Run tests in parallel (local)
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Run tests in parallel (CI)
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Test Distribution
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Test Distributor
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Test Distribution Results
‑ ~50%
‑ ~50%
‑ ~50%
Doubling the number of executors cuts build time in half
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Let’s use AI!
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“The test selection procedure selects fewer than a
third of the tests that would be selected on the basis of
build dependencies”
Predictive Test Selection - Meta Research
https://research.facebook.com/publications/predictive-test-selection/
Mateusz Machalica, Alex Samylkin, Meredith Porth, Satish Chandra
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Predictive Test Selection time savings
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What if we just make our tests faster?
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Like any performance problem,
focus on the worst-performers first
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“Once things like databases become a hindrance,
optimise the testing loop, mock things out to run
things fast. You can run locally and you don't have all
the same infra dependencies as someone else.”
On DevEx, PaaS, and Testing in Production https://bit.ly/3ZA0uQM
Kelsey Hightower
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Look out for expensive setup and
tear down
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Invent Time Travel
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Write Better Tests
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⬢ Separation of concerns
⬢ Encapsulation
⬢ High cohesion and loose coupling
⬢ SOLID
⬢ DRY
⬢ Descriptive naming
⬢ Modularisation
⬢ Designing for performance
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Tension between these ideals
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Refactor and Delete
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“Yes, I regularly delete tests that no longer add unique
value.”
Angie Jones (@techgirl1908)
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Summary
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Automate as much as possible
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Tooling can help you
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There is a time investment in writing tests,
because there should be thinking involved
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Invest time in writing better tests.
They will be easier to debug, less flaky, and
better document your system’s expected behaviour
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“Testing is not only for checking the system does what
it’s supposed to, it’s for documenting the expected
behaviour.”
Israel Boza Rodriguez (@IsraKaos)
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bit.ly/3MGAMnZ
bit.ly/slow-tests
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