Why do Quarkus tests fail in Eclipse after upgrade to new LTS version?

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Summary

Quarkus tests fail in Eclipse after upgrading because Quarkus 3.22+ introduced a rewritten test classloading system, and Eclipse’s built‑in JUnit launcher is not yet fully compatible with the new QuarkusClassLoader expectations.

Root Cause

  • Quarkus 3.22 introduced a major rewrite of the test classloading internals, specifically affecting @QuarkusTest.
  • Eclipse still launches tests using the standard AppClassLoader, not the QuarkusClassLoader required by the new test infrastructure.
  • The FacadeClassLoader fails to detect the test as a Quarkus test, causing the runtime error you observed.

Why This Happens in Real Systems

  • IDEs often lag behind framework-level classloader changes.
  • Quarkus uses complex, multi‑stage classloading to simulate the dev/test environment, which is fragile when IDEs bypass the intended bootstrap path.
  • Upgrades that modify classloading internals frequently break assumptions made by IDE test runners.

Real-World Impact

  • Tests run fine via Maven/CLI but fail inside Eclipse, causing:
    • Broken local workflows
    • Inconsistent test results between developers
    • Confusion due to tests passing in CI but failing in the IDE
    • Time lost debugging non‑application issues

Example or Code (if necessary and relevant)

A typical failing test looks like this:

@QuarkusTest
class FooBarTest {
    // test code
}

Running this in Eclipse triggers the error because Eclipse loads it with the AppClassLoader instead of the QuarkusClassLoader.

How Senior Engineers Fix It

  • Run tests via Maven or Gradle until Eclipse updates its Quarkus tooling.
  • Use the Quarkus CLI (quarkus test) which correctly initializes the QuarkusClassLoader.
  • Update Eclipse Quarkus and JDT extensions to the latest available versions.
  • Switch to IntelliJ or VS Code temporarily if IDE‑integrated Quarkus testing is critical.
  • Track the upstream issue in the Quarkus GitHub repository to know when a fix lands.

Why Juniors Miss It

  • They assume IDE test runners behave the same as CLI builds, which is not true for Quarkus.
  • They often don’t understand classloader boundaries, especially Quarkus’s layered model.
  • They expect that upgrading a framework is isolated, not realizing IDE integrations must also evolve.
  • They may not read release notes that mention breaking changes in test infrastructure.

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