We all know that fast feedback loops make a real difference and that they are the most important part of agile development in general. This is why I want to take you on a tour of a variety of ways to increase quality and optimize feedback loops that I’ve encountered in the JVM-based projects that I’ve worked on so far.

1. Michał Kordas
Blazing Fast Feedback Loops
in the Java Universe

2. FEEDBACK
DO A THING
CHECK HOW
IT WENT
DO NOT BUILD ON ASSUMPTIONS

5. CONTEXT
• Small team
• All use IntelliJ IDEA
• ~30 repositories
• Java, Groovy, Scala
• Maven, Groovy
• Jenkins
• GitHub

6. WHAT YOU DO WHEN…?
• broken environment
• not meaningful exception
• struggling with technology
• struggling with project
• style-related comment during code review

7. EVERY TIME WHEN
FEEDBACK COMES TOO
LATE TRY TO MAKE IT
FASTER

8. BROKEN ANYTHING?
ADD A HELL LOT OF HEALTH CHECK BUILDS

9. NOT MEANINGFUL EXCEPTION?
FAIL FAST
CATCH EXCEPTION OR THROWABLE
ADD CONTEXT
AND RETHROW OR YOU’LL DIE

10. STRUGGLING WITH TECHNOLOGY?
ASK ON STACKOVERFLOW
(AND ANSWER BY YOURSELF)

11. STRUGGLING WITH PROJECT?
ADD TO KNOWLEDGE BASE
README.md wiki

12. STYLE ISSUES DURING CODE REVIEW?
ADD TASK TO AUTOMATE NEXT TIME

13. COMPILER WARNINGS
http://programmers.stackexchange.com/questions/94754/how-do-i-
convince-my-teammates-that-we-should-not-ignore-compiler-warnings

14. COMPILER WARNINGS

15. PREVENTING COMPILER WARNINGS

16. DEPENDENCY UPDATES

17. MONITORING DEPENDENCY UPDATES
MAVEN
GRADLE
HOW?
• tool that invokes the above commands in all repositories
• report for developers is created periodically

18. COMMIT MESSAGES
"git log origin/master..HEAD".execute().text

19. BUILD STATUS

20. JENKINS CI BUILD MONITOR PLUGIN
https://github.com/jan-molak/jenkins-build-monitor-plugin

21. SIREN OF SHAME
https://sirenofshame.com/

22. GITGUARD
Chrome extension blocking GitHub merge
button based on specified Jenkins jobs
https://chrome.google.com/webstore/detail/
gitguard/dlbacfedgdjanlkofjckclmgmijbhakl

23. NO RED MASTER PLEASE!
• Run all tests on branches
• Use GitHub Status API
• Merge master before running tests

24. ENFORCE UP-TO-DATE
• Enforce branch to be up-to-date before
merge

25. SHIELDS AND BUTTONS

26. UNIT TESTS
Fast (hundreds per second, run in parallel)
Isolated (single unit tested)
Repeatable (always the same result)
Self verifying (either pass or fail)
Timely (written early)
FIRST
BLAZINGLY FAST AND ULTIMATELY RELIABLE TESTS
mvn test gradlew test SHIFT+F10

27. PARALLEL TESTS CONFIGURATION

28. PARALLEL BUILD CONFIGURATION

29. GRADLE PERFORMANCE TIPS
mavenCentral() jcenter()
USE DAEMON
UPDATE TO LATEST GRADLE
gradlew wrapper –gradle-version 3.1
gradlew build --profile
USE JCENTER
PROFILE
GRADLE BUILD SCANS
COMPILE INCREMENTALLY
compileJava.options.incremental = true

30. CODE STYLE / STATIC ANALYSIS
• Checkstyle, PMD, FindBugs, CodeNarc
• Agree on common rules for all projects
• Shared configurations
• Gradle plugin
• Maven plugin
• Maven parent POM (tricky)

31. INTERNAL QUALITY PLUGIN
• Integrates all agreed tools with all
reasonable rules enabled
• Customized for project/company needs
• Zero configuration by default
• Unified console output with clickable links
gradlew checkstyleMain pmdMain findbugsMain codenarcMain
checkstyleTest pmdTest findbugsTest codenarcTest
gradlew quality

32. BLACKLISTS
• Use blacklists instead of whitelists to get
new rules
PMD
FindBugs
CodeNarc

33. EARLY STATIC ANALYSIS FEEDBACK
• CheckStyle-IDEA
• FindBugs-IDEA
• SonarLint

34. GATHER VIOLATIONS FROM ALL TOOLS
AND MODULES
gradlew quality --continue
mvn -fae
mvn --fail-at-end

35. GRADLE BASE PLUGIN
• Applies ‘java’, ‘groovy’ and ‘maven’ plugins
• Always shows full stacktraces, even if --stacktrace is forgotten
• Adds provided configuration (missing in Gradle)
• Configures repositories with dependencies
• Adds tuned compiler configuration for Java and Groovy
• Displays detailed information about all warnings (-Xlint:all option)
• Fails build on any unsuppressed warning (-Werror option)
• Adds configuration to run tests in parallel
• Enables rich test logging with summary
• (Tests run: 3, Failures: 2, Skipped: 1) and full stacktraces
• Configures wrapper task with latest Gradle
• Applies taskTree plugin
• Applies com.github.ben-manes.versions plugin
• Prints Gradle and JVM versions in the output

36. SANITY BUILD MATRIX
Periodically run on master series of builds using
different configurations that developers may use
• various Java and Maven versions
• various build parameters like -DskipTests
• various JVM params like locale
• compilation with fresh repository

37. MUTATION TESTING
• Mutations are made to the code
• If tests fail then the mutant is
• If tests pass then the mutant
• Percentage of mutants killed is indicator of
your tests quality
• Can be really
killed
lived
slow!

38. FAST MUTATION TESTING
scmMutationCoverage
GitHub status
Report

39. NON-REQUIRED CHECKS
https://help.github.com/articles/about-required-status-checks/

40. NONDEX
• Tool for detecting wrong assumptions
about Java APIs
• assuming specific order of HashMap iteration
• Run tests with changed implementations of
standard classes to return shuffled results
• Same happens when upgrading Java

41. APIS ANAYZED BY NONDEX

42. PLAY WITH COMMITTING .IDEA FILES

43. PROVISION NODES AUTOMATICALLY

44. GET STATUS ON PULL REQUESTS
QUICKLY

45. PIPELINES
https://wiki.jenkins-ci.org/display/JENKINS/Build+Pipeline+Plugin
gradlew build

46. CODE REVIEW
• Do timely
• Assign people
• Internal team review
• External review
• Address comments

47. OPEN PULL REQUESTS DASHBOARD
https://github.com/pulls

48. CONTRIBUTING FILE
create CONTRIBUTING.md in repository root
be notified

49. QUALITY OF FEEDBACK

50. RETROSPECTIVES

51. RETROSPECTIVES
IF IT IS NOT FUN, YOU'RE DOING IT WRONG

52. DIALOGUE SHEETS
https://www.softwarestrategy.co.uk/dialogue-sheets/

53. CONSTANT IMPROVEMENT

54. SUMMARY
• We want feedback to
• continuously improve
• deliver more value
• reduce risk
• learn
• Feedback has
• many types
• many sources

55. THERE IS NO FAILURE.
ONLY FEEDBACK.
Robert Allen