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

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2. @rieckpil
   Things I Wish I Knew When I
   Started Testing Spring Boot
   Applications
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3. @rieckpil
   My (Not So Effective) Introduction to Testing
   3
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4. @rieckpil 4
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5. @rieckpil
   Getting Used To Testing At Work
   5
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6. @rieckpil
   Getting Used To Testing At Work - Part II
   6
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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
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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
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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
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10. @rieckpil
    The Testing Swiss-Army Knife
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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
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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
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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
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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
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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
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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
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17. @rieckpil
    What’s Inside the Testing Toolbox
    JSONAssert
    - Assertion library for JSON data
    structures
    - Compare entire JSON objects
    - Strict and nonstrict assertions
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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
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19. @rieckpil
    Spring Boot’s Dependency Management
    - Spring Boot manages the
    dependency version of further
    testing libraries
    - Examples: Awaitility, Selenium,
    MockWebServer (from OkHttp)
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    - 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
    

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20. @rieckpil
    @SpringBootTest Isn’t Always Your Friend
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21. @rieckpil
    The Auto-Generated @SpringBootTest Test
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22. @rieckpil
    Understanding @SpringBootTest
    22
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    - 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
    

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23. @rieckpil
    Understanding @SpringBootTest
    23
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    - 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.
    

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24. @rieckpil
    @SpringBootTest Obsession
    24
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    Testing every single
    class with
    @SpringBootTest
    … results in a lot
    of different
    context setups
    and slows down
    the build
    

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25. @rieckpil
    @SpringBootTest Obsession: Slower Test Suite
    25
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    Testing ServiceOne
    with @SpringBootTest
    Testing ServiceTwo
    with @SpringBootTest
    

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26. @rieckpil
    @SpringBootTest Obsession
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27. @rieckpil
    Slicing aka. You May Not Always Need
    the Entire Context
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29. @rieckpil 29
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    Creating a much
    smaller context
    with only relevant
    beans
    

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30. @rieckpil
    Sliced Test Context Example: @WebMvcTest
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    - 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
    

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31. @rieckpil 31
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32. @rieckpil 32
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33. @rieckpil
    JUnit 4 vs. JUnit 5 Pitfall
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34. @rieckpil
    JUnit 4 vs. JUnit 5 Pitfall
    34
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    - 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
    

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35. @rieckpil
    Indicators to Differentiate the Version
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    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
    

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36. @rieckpil
    Where To Go Next?
    36
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    - 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
    

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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/
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38. @rieckpil
    Conclusion
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    - 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
    

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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 🥳
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