feat(core): Adding a fake LLM with tool calling capabilities for easy integration with LangGraph

[sijil-salim]

Added a new Fake LLM in lines of FakeListChatModel to return tool calls so that it is directly compatible with LangGraph. This fake LLM can be used for testing LangGraph workflows

[vercel]

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Name	Status	Preview	Comments	Updated (UTC)
langchain	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Jul 28, 2025 11:08pm

[sijil-salim]

@eyurtsev Hi, I pushed a change for adding a fake llm with tool building capabilities yesterday. However, the deployment got skipped and got a message from verbal with links which upon opening shows Vercel error page. Can you please help me with what might have gone wrong and how I can rectify it

[eyurtsev]

Will review a bit more carefully later, but we don't want another implementation. Instead one of the existing implementations should be enhanced properly

[codspeed-hq]

CodSpeed WallTime Performance Report

Merging #32002 will not alter performance

_{Comparing sijil-salim:fake-llm-with-tool-calling (52ae5b0) with master (0b56c1b)}

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

Summary

✅ 13 untouched benchmarks

[codspeed-hq]

CodSpeed Instrumentation Performance Report

Merging #32002 will not alter performance

_{Comparing sijil-salim:fake-llm-with-tool-calling (52ae5b0) with master (0b56c1b)}

Summary

✅ 6 untouched benchmarks
🆕 2 new benchmarks
⁉️ 6 dropped benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
🆕	test_init_time	N/A	6.6 s	N/A
🆕	test_init_time	N/A	1.6 s	N/A
⁉️	test_stream_time	1.1 s	N/A	N/A
⁉️	test_stream_time	519.5 ms	N/A	N/A
⁉️	test_stream_time	1.1 s	N/A	N/A
⁉️	test_init_time	1.7 s	N/A	N/A
⁉️	test_init_time	17.1 ms	N/A	N/A
⁉️	test_init_time	17.1 ms	N/A	N/A