feat: integration tests for java generator

feat: integration tests for java generator

Description

The CLI has adopted an integration testing pattern to validate that generated feature flag clients compile and function correctly within their respective language ecosystems. The Java generator does not yet have integration test coverage.

We should implement integration tests for the Java generator using the standardized approach outlined in the test suite documentation.

📄 Relevant Documentation:
Integration Testing Pattern

Tasks

• Create a test project scaffold for Java (e.g., using Maven or Gradle)
• Generate a feature flag client using the Java generator
• Compile and execute basic assertions (e.g., ensure the generated code builds, dependencies resolve, and a simple flag evaluation runs)
• Integrate this test into the broader test suite and CI workflow
• Add any Java-specific test setup or notes to the documentation if needed

Acceptance Criteria

• ✅ Java generator is covered by at least one integration test
• ✅ Generated Java code compiles and passes basic execution
• ✅ Integration test runs as part of the CI suite
• ✅ Test follows the documented integration testing structure

Additional Notes

Adding Java integration tests ensures that changes to the generator do not silently introduce regressions and increases confidence in the CLI's language support matrix.

Start with test/README.md and its documented integration testing structure. Create the Java test project, generate a client with the Java generator, compile and run basic flag-evaluation assertions, then integrate the test into the broader test suite and CI workflow. Done means the generated Java code builds, executes successfully, and runs in CI.