test_stream

First, debug langchain_tests.integration_tests.chat_models.ChatModelIntegrationTests.test_invoke. because stream has a default implementation that calls invoke and yields the result as a single chunk.

If that test passes but not this one, you should make sure your _stream method does not raise any exceptions, and that it yields valid langchain_core.outputs.chat_generation.ChatGenerationChunk objects like so:

yield ChatGenerationChunk(message=AIMessageChunk(content="chunk text"))

The final chunk must have chunk_position='last' to signal stream completion. This enables proper parsing of tool_call_chunks into tool_calls on the aggregated message:

for i, token in enumerate(tokens):
    is_last = i == len(tokens) - 1
    yield ChatGenerationChunk(
        message=AIMessageChunk(
            content=token,
            chunk_position="last" if is_last else None,
        )
    )