How we've built Yahoo Fantasy Football in the Yahoo UK office. Presented at Droidcon Italy 2015, in Turin, on April 10th.

1. HOW WE’VE BUILT
YAHOO FANTASY FOOTBALL
Alex Florescu
Yahoo UK
#droidconit
April 10th, 2015

2. OVERVIEW
Intro
Principles & practices
Testing
Internationalisation
Instrumentation & A/B testing
Performance

3. INTRO
London team started in January 2014
Fantasy Football (Fantasy Calcio) launched in July 2014
Android / iOS / Web clients + back-end team

4. THE APP
100k+ MAUs (on Android), ★★★★☆
Premier League, Campionato Italiano, Ligue 1©, Bundesliga, La Liga, MLS

5. KEY PRINCIPLES
Automate everything
Short release cycle
Performance, stability, quick changes
Track and measure everything
Data-driven product decisions
Stress and enforce principles, not process

6. ENGINEERING PRACTICES - CI
CI pipeline from day one
CD up to internal deployment
Unit testing & UI testing
Automatic APK generation and signing
Compile time configs for dev, dogfood & production builds

7. ENGINEERING PRACTICES - CI
Git flow: Work on a branch, do a pull request to merge
Short lived branches, keep PRs brief
Master always builds, always shippable
All code must be reviewed
Compile-time feature toggles “disable” code that is not ready

8. TESTING
CI without automated testing is …
Different levels of testing
On commit hook: robolectric suite
Next stage, smoke suite of UI tests
Nightly: full suite of UI tests, performance tests, monkey tests

9. ROBOLECTRICTESTING
Robolectric tests run on JVM, no devices needed
Slower than plain JUnit tests, but significantly faster than UI tests
Very useful as unit tests
With architectures such as MVP, can also be acceptance tests

10. ROBOLECTRIC PROBLEMS
Not all Android framework functionality is replicated
Differences between JVM and DalvikVM
Difficult to test complex user flows over multiple screens
Custom views sometimes problematic

11. OUR NUMBERS
700+ tests
50-60% coverage (higher in biz logic, lower in UI)
2’ to run, 6’ full build from scratch

12. UITESTS
Good:
Proper integration tests
Run on device
Most closely resembling real user flows
Can catch device specific issues

13. UITESTS
Bad:
Synchronisation problems (e.g. Button “OK” not found)
Brittle, hard to maintain
Very slow to run
Requires a device lab to be setup for CI

14. SMOKE SUITEVS FULL SUITE
Even small suites can take hours to run because of sync issues
For sanity checking, a smoke suite will do
Relatively fast (10-15min) & simple UI test
Ensure app runs and can see all screens

15. FULL SUITE
For enhanced testing, a nightly full suite
In-depth user flow tests, can run for
hours
Make sure someone checks it daily!
Should be a release blocker

16. CI PIPELINE

17. MONKEYTESTING
Useful for stability testing
Catches crashes and memory leaks
Could be included in automated nightly runs
Make sure app activity is restricted
Lock monkey in app (e.g. Surelock)
Consider removing certain features when monkey runs

18. TRACKINGTESTING
Coverage useful for analysis (e.g. what areas get the least testing
and why?), but should not enforce a coverage target
Reasonable to expect acceptance tests with features
Enforce testing through code review
Tests are code!
Refactoring, good architecture, documentation, still apply

19. I18N, L10N …
Translation: strings only
Localisation: adapting content for language, culture and region
Internationalisation: designing a product to allow localisation

20. CALCIO, SOCCER, FUßBALL…
We shipped to 20+ locales from day one
Challenges:
All strings needs to be translated
Number formatting, currency formatting etc.
Support, reviews, release notes
Testing load increased — UI issues with some locales only

21. I18N — DEALING WITH IT
Externalise all strings and enforce no lint errors on build
Collect all strings early for translation before they block release
Have standard release notes saved & translated for emergencies
Some test devices permanently on tricky locales

22. I13N — INSTRUMENTATION
What
Collecting data to understand how an app performs and how it
is used
Why
Key to understanding what the users are doing

23. WHATTO INSTRUMENT
Time spent in app
Buttons tapped
Loading time, network performance
Anything you want!

24. WHATTO DO WITH DATA
How long does it take a user to create a team?
What are the best triggers for a user to sign in?
How often do users share something with friends?
Signs of frustration: e.g. repeating identical action

25. 13N CHALLENGES
Collecting the data is the easy part (and it’s not easy)
Don’t reinvent the wheel, use 3rd party tools for this
We use Flurry
Real challenge:
What does user engagement mean? How do you measure it?

26. A/BTESTING — WHY?
What makes users more likely to invite or share with friends?
What makes users more likely to be engaged? Happy?
What features do we add or remove?
Is a new feature supporting our high level goals?
Goal: maximum user satisfaction and engagement with minimum
number of features

27. EXPERIMENTS
Build-up an MVP of your new feature
Enabled the feature in a test bucket (e.g. only for 10% of users)
Data is collected for all users, bucket-aware and results are
compared across test and control bucket
Results can be used to guide product decisions

28. EXPERIMENT EXAMPLE
Hypothesis:A prompt to
share the newly created
league will increase the
number of shares

29. EXPERIMENT RESULTS
Succesful!
71% of users that see the prompt share the league

30. EXPERIMENT EXAMPLE
Hypothesis: A tutorial will
increase the number of
completed teams

31. EXPERIMENT RESULTS
Completion team was actually unaffected: hypothesis rejected
But, significantly more likely that they will complete the team in
the same session

32. EXPERIMENTS
“Guesses” are not necessarily right
“Obvious” improvements may not be
Used correctly, real world data provides proof

33. PERFORMANCE
Caring is measuring
What numbers we track
Cold start time
FPS
Automated measurements (e.g. nightly build to track progress)
Track production numbers — this is what matters

34. PERFORMANCE
Numbers will vary wildly in different regions
Slower networks, older devices
When we started monitoring our world average for load time
was ~2-3x our US/UK one

35. PERFORMANCE

36. WRAP-UP
CI & automated testing are key for quality and stability
Instrument everything, use data to experiment and guide product
A/B testing can confirm product hypothesis
You should localise your apps, but know what you’re getting into
Performance needs prod monitoring and on-going measurement

37. Q & A
yahoo-mep.tumblr.com
www.florescu.org
@flor3scu