What's wrong with AssertJ?!

https://www.jug.ch/html/events/2026/assertj.html

Transcript

1. Stefano Cordio M a y 1 2 t h , 2 0 2 6 What’s Wrong with AssertJ?! How a decade of technical debt is addressed in version 4
3. $ whoami Lead Software Engineer Technical Lead @ Large Swiss Bank
4. $ whoami
5. What is AssertJ?
6. Java Assertion Library Fluent API Type-specific Assertions
7. Designed around IDE auto-completion
8. Helpful Error Messages
9. Javadoc with Examples
10. Coordinates assertj/assertj <dependency> <groupId>org.assertj</groupId> <artifactId>assertj-core</artifactId> <version>3.27.7</version> <scope>test</scope> </dependency> testImplementation("org.assertj:assert-core:3.27.7")
11. Most Popular Assertion Library
12. Trusted by Popular Open Source Projects JUnit 5 Mockito Spring Framework Spring Boot LangChain4j
13. AssertJ Core AssertJ Guava AssertJ Generator joel-costigliola Joel Costigliola scordio Stefano Cordio AssertJ Vavr Grzegorz Piwowarek pivovarit AssertJ DB VanRoy Julien Roy AssertJ Neo4j Florent Biville fbiville AssertJ Swing Christian Rösch croesch Matt Bertolini mattbertolini AssertJ Eclipse Collections Riccardo Cardin rcardin AssertJ Arrow Core AssertJ Protobuf The Team filiphr Filip Hrisafov Nava2 Kevin Brightwell
14. So, What’s Wrong with AssertJ?!
15. The AssertJ History FEST Assert 1.x 2.x 3.x 4.x 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2027 2026 1.0 1.4 1.0 1.7.1 2.0 2.9.1 3.0 3.27.7 Fork! 3.28 2.3 2.6 2.7 2.9 3.3 3.6 3.8 3.10 3.13 3.17 3.20 3.22 3.24 3.26 3.27 1.6 Java 8 Java 17 Java 7 4.0-M1 4.0 4.0-M2
16. Entry Points
17. Entry Points
18. Inconsistent Return Types
19. Inconsistent Return Types
20. Inconsistent Return Types Abstract classes → Contracts Name without “Abstract” Concrete classes → Implementation details Never public, controlled instantiation via factory methods
21. Soft Assertions
22. Soft Assertions Performance penalty due to proxying at runtime with Byte Buddy Alternatives: • Byte Buddy proxying at compile time • Source code generation (JavaPoet, Java Template Engine) • Explicit wrapping logic ✓ Recently contributed by filiphr Filip Hrisafov
23. Kotlin Interoperability
24. Groovy Interoperability
25. What Else to Expect?
26. 3.x → 4.0 Migration with OpenRewrite Assertions for New JDK Classes Multi-release JAR to support JDK types > 17 Diff-like Error Messages for Strings and Collections MCP Server for LLM Integration? AssertJ Incubator?
27. User Guide with Antora Javadoc Markdown and Executable Snippets Integration Testing with Popular Projects (Spring, JUnit, Mockito, etc.)
28. We Want to Hear from You!
29. Get in touch at assertj/assertj Use Cases • Missing Features • Friction Try Out Milestone Versions
30. Open Source in Switzerland 5th June 2026 Technopark Winterthur winterthur2026.hack-commit-pu.sh Monthly evenings Zürich / Luzern / Basel www.hackergarten.net
31. Thank you!