test: add langchain-google-genai integration tests for RAI features (…

[Ranga-Prasath-22]

…#168)

This test suite verifies the integration and functionality of the ChatGoogleGenerativeAI model, including initialization, invocation, error handling, and support for model variants.

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[maciejmajek]

Thank you for the contribution! I appreciate the effort you put into adding tests for Google GenAI integration.

A few points to note:

• The PR does not add the langchain-google-genai dependency, so these tests won’t run out of the box.
• The added tests are heavily mocked. While they might make sense for testing the LangChain package itself, they don’t really test RAI, which uses LLMs in a less conventional way. Fully mocked tests like these don’t provide much value here.
• For RAI, testing LLM integrations works better through manual testing. Before configuring the model in config.toml, the initialization module should be updated to support the new LLM vendor. Then you can manually test by running the demos to verify everything works as expected.

Just so you know, our current contributor @sachinkum0009 is also working on Google GenAI integration. You could coordinate to pick up the work together or test the capabilities separately.

Thanks again!