JUnit awareness for mixed stacks

JUnit is the standard JVM test framework—`@Test`, lifecycle annotations, assertions, and Spring Test integration. Full-stack JS roles touch JVM services when BFF calls Java microservices or monorepos mix Kotlin backends with React frontends.

You rarely implement JUnit daily, but you should read failures, know integration tests use `@SpringBootTest`, and respect that provider contract tests may run in Java CI.

On interviews: explain how you'd coordinate a Pact or API change across Node consumer and Java provider pipelines.

Common pitfalls: assuming Jest patterns map 1:1 to JUnit extensions, ignoring Java CI as source of truth for shared APIs.

The trade-off is shallow JVM literacy versus over-investing in a stack you do not own.

Checklist:

• Recognize JUnit test class structure and annotations.
• Know where JVM integration tests live in your org.
• Coordinate cross-language contract failures.