Things I Wish I Knew When I Started Testing Spring Boot Applications

Getting started with Spring Boot and its auto-configuration mechanism can be a hurdle for new developers.

Once you get your first Spring Boot application up- and running, writing tests for it is the last thing you care about. You’re happy that your code does its job.

However, as soon as you try to integrate your changes, you face a pull request rejection because your lead developer reminds you that tests are missing.

Testing is an integral part of software development, and unfortunately, some teams treat this topic neglectfully. That’s bad for the future maintenance and overall health of their project. Fortunately, both Spring Test and Spring Boot offer excellent support for testing your application.

This talk will give you an overview of best practices, pitfalls, and recipes for testing Spring Boot applications. Simply put, with this talk, I’ll share the things that I wish I had known when I started testing Spring Boot applications.

Transcript

2. @rieckpil Things I Wish I Knew When I Started Testing Spring Boot Applications 🍃
3. @rieckpil My (Not So Effective) Introduction to Testing 3 🍃
4. @rieckpil 4 🍃
5. @rieckpil Getting Used To Testing At Work 5 🍃
6. @rieckpil Getting Used To Testing At Work - Part II 6 🍃
7. @rieckpil Goals for This Talk Lay the foundation for your Spring Boot testing success Introduction to Spring Boot’s excellent test support Convince you that testing is not an afterthought Showcase a mix of best practices and early pitfalls 7 🍃
8. @rieckpil Agenda for This Talk 1. Introduction 2. Things I Wish I Knew When I Started a. The Testing Swiss-Army Knife b. @SpringBootTest Isn’t Always Your Friend c. Slicing aka. You May Not Always Need the Entire Context d. JUnit 4 vs. JUnit 5 Pitfall 3. Where to Go Next? 4. Conclusion and Q&A 8 🍃
9. @rieckpil About Me - Freelance IT consultant from Berlin, Germany - Enjoys writing blog posts on rainy days in cozy cafes (#TeamWordPress) - Blogging & content creation for more than five years. Since two years with a focus on testing Java and specifically Spring Boot applications - Co-authored Stratospheric - Form Zero to Production With Spring Boot and AWS together with Björn Wilmsmann (@bwilmsmann) and Tom Hombergs (@TomHombergs) - Blog: https://rieckpil.de - GitHub: https://github.com/rieckpil/ - YouTube: https://www.youtube.com/c/rieckpil 9 🍃
10. @rieckpil The Testing Swiss-Army Knife 10 🍃
11. @rieckpil Your Testing Foundation - The Spring Boot Starter Test aka. “Testing Swiss-Army Knife“ - Part of every Spring Boot project - Includes everything you need to get started with testing Spring Boot applications 11 🍃
12. @rieckpil Introspecting the Swiss-Army Knife - Opinionated testing toolbox - Upgrade their versions consistently when upgrading Spring Boot - Unless there are no conflicts, no need to exclude unused libraries as they don’t end up in the production JAR 12 🍃
13. @rieckpil What’s Inside the Testing Toolbox - Core testing framework - Successor and rewrite of JUnit 4 - Extension model, test parallelization, dynamic tests, parametrized tests, etc. 13 🍃
14. @rieckpil What’s Inside the Testing Toolbox - Java’s de-facto standard mocking library - Mock collaborators, stub their behavior and verify their interaction for testing purposes 14 🍃
15. @rieckpil What’s Inside the Testing Toolbox AssertJ - Assertion library with matchers for many types: collections, temporals, etc. - Fluent and sentence-like assertions - Write your own custom assertions 15 🍃
16. @rieckpil What’s Inside the Testing Toolbox Hamcrest - Fluent assertion library - Occasionally used within Spring Test, e.g. MockMvc verifications - Implementation for many other programming languages 16 🍃
17. @rieckpil What’s Inside the Testing Toolbox JSONAssert - Assertion library for JSON data structures - Compare entire JSON objects - Strict and nonstrict assertions 17 🍃
18. @rieckpil What’s Inside the Testing Toolbox JsonPath - Extract data from JSON for further assertions using JsonPath expressions - Use an assertion library of your choice for verifying the extracted information 18 🍃
19. @rieckpil Spring Boot’s Dependency Management - Spring Boot manages the dependency version of further testing libraries - Examples: Awaitility, Selenium, MockWebServer (from OkHttp) 19 🍃 - Up- or downgrade the version of a managed testing library version - Check the spring-boot- dependencies project for a list of managed libraries and their versions
20. @rieckpil @SpringBootTest Isn’t Always Your Friend 20 🍃
21. @rieckpil The Auto-Generated @SpringBootTest Test 21 🍃
22. @rieckpil Understanding @SpringBootTest 22 🍃 - Populates the entire ApplicationContext based on the @SpringBootApplication class - Best suited for integration tests - Starting your entire application requires access to all dependent infrastructure components
23. @rieckpil Understanding @SpringBootTest 23 🍃 - Starts the embedded servlet container (e.g. Tomcat) - Auto-configures the WebTestClient/TestRestTemplate - Inject the port with @LocalServerPort - Starts the application with a mocked servlet environment - No real HTTP communication - Use MockMvc to interact with the application’s endpoint vs.
24. @rieckpil @SpringBootTest Obsession 24 🍃 Testing every single class with @SpringBootTest … results in a lot of different context setups and slows down the build
25. @rieckpil @SpringBootTest Obsession: Slower Test Suite 25 🍃 Testing ServiceOne with @SpringBootTest Testing ServiceTwo with @SpringBootTest
26. @rieckpil @SpringBootTest Obsession 26 🍃
27. @rieckpil Slicing aka. You May Not Always Need the Entire Context 27 🍃
28. @rieckpil 28 🍃
29. @rieckpil 29 🍃 Creating a much smaller context with only relevant beans
30. @rieckpil Sliced Test Context Example: @WebMvcTest 30 🍃 - Testing our controller endpoints in isolation - No real HTTP communication but a mocked servlet environment (MockMvc) - Integration with Spring Security to verify protection and authorization
31. @rieckpil 31 🍃
32. @rieckpil 32 🍃
33. @rieckpil JUnit 4 vs. JUnit 5 Pitfall 33 🍃
34. @rieckpil JUnit 4 vs. JUnit 5 Pitfall 34 🍃 - JUnit 5 is a redesign of JUnit 4, and the next generation of JUnit - First release of JUnit 5 in 2017 - JUnit 5 = JUnit Platform (foundation and TestEngine API) + JUnit Jupiter (new programming model) + JUnit Vintage (TestEngine to run JUnit 3 and 4 tests) - We can’t mix both versions within the same test - We can run JUnit 4 and 5 tests next to each other thanks to the JUnit Vintage engine - For automatic migration support, see OpenRewrite
35. @rieckpil Indicators to Differentiate the Version 35 🍃 JUnit 4 - @Test from org.junit - @RunWith - @Rule/@ClassRule - @Before/@BeforeClass - @After/@AfterClass - @Ignore - @Category JUnit 5 - @Test from org.junit.jupiter.api.test - @ExtendWith/@RegisterExtension - @BeforeEach/@BeforeAll - @AfterEach/@AfterAll - @Disabled - @Tag
36. @rieckpil Where To Go Next? 36 🍃 - Get familiar with the sliced test context annotations that fit your use case - Align the test strategy and vocabulary for your project - Take some time to learn and understand Spring Boot’s auto-configuration - Give Test-Driven Development (TDD) a try - Get familiar with your core testing tools: JUnit & Mockito - Explore further Java testing libraries like Testcontainers, WireMock, and Selenide
37. @rieckpil Testing Spring Boot Applications Masterclass - Testing real-world Spring Boot applications - 130+ course lessons with 10h+ hands-on video content - Tech-Stack: Spring Boot 2.7, PostgreSQL, React 18, Java 17, Keycloak (OAuth 2 login), communication with a remote HTTP system, async workflows with a messaging queue (Amazon SQS) - Techniques, pitfalls, and patterns for unit, integration, and end-to-end testing - Best of breed testing tools: JUnit 5, Mockito, LocalStack, Testcontainers, Awaitility, WireMock, MockWebServer, Selenide, etc. - https://rieckpil.de/testing-spring-boot-applications-masterclass/ 37 🍃
38. @rieckpil Conclusion 38 🍃 - Spring Boot provides a lot of excellent testing tools and emphasizes testing - Every Spring Boot project comes with a fundamental testing toolbox - Ask yourself: “Do I really need to start the entire context for this test?” - Use @SpringBootTest for integration tests - A sliced context lets you test a specific part in isolation - When applying test recipes from other projects (aka. Stack Overflow), check the used JUnit version - Have fun writing your tests
39. @rieckpil Q&A Questions? Slides will be uploaded ✅ The best way to get in contact is via Twitter @rieckpil 👋 Visit my blog for more testing-related Spring Boot content 🧪 Enjoy the rest of the conference 🥳 39 🍃