Add characterization tests for basic langchain text responses and stream data.

[lgrammel]

Overview

• Introduce x-flush-delay header in mock server to speed up tests (default to 5ms to speed up existing tests)
• Introduce port configuration for mock server to allow running several tests in parallel
• Add langchain dev dependency
• Add langchain characterization tests for existing behavior based on examples from website

Note

The langchain stream test does not work in the edge environment and is deactivated in that environment. The errror is caused by the following chain of events:

• langchain functionality is required for langchain integration testing, so I added a dev dependency
• langchain is used in other parts of the project, therefore the dependencies become non-dev dependencies in the lockfile
• langchain has a dependency on uuidjs/uuid
• uuidjs/uuid has an open bug with their dist: [BUG] Unexpected token 'export' with Jest (on Cloudflare Workers) uuidjs/uuid#678 (that’s open for almost a year)
• the edge environment testing does not compile with

Details:

    /Users/lgrammel/repositories/vercel-ai/node_modules/.pnpm/uuid@9.0.0/node_modules/uuid/dist/esm-browser/index.js:1
    ({"Object.<anonymous>":function(module,exports,require,__dirname,__filename,jest){export { default as v1 } from './v1.js';
                                                                                      ^^^^^^

    SyntaxError: Unexpected token 'export'

[lgrammel]

With Langchain, there is an empty text chunk at the beginning and the end. Is this desired?

[MaxLeiter]

No, but it shouldn't be a problem and not worth investigating until we finalize the complex mode API imo

[lgrammel]

The error is caused by the following chain of events:

• langchain functionality is required for langchain integration testing, so I added a dev dependency
• langchain is used in other parts of the project, therefore the dependencies become non-dev dependencies in the lockfile
• langchain has a dependency on uuidjs/uuid
• uuidjs/uuid has an open bug with their dist: [BUG] Unexpected token 'export' with Jest (on Cloudflare Workers) uuidjs/uuid#678 (that’s open for almost a year)
• the edge environment testing does not compile with

    Details:

    /Users/lgrammel/repositories/vercel-ai/node_modules/.pnpm/uuid@9.0.0/node_modules/uuid/dist/esm-browser/index.js:1
    ({"Object.<anonymous>":function(module,exports,require,__dirname,__filename,jest){export { default as v1 } from './v1.js';
                                                                                      ^^^^^^

    SyntaxError: Unexpected token 'export'

I’ve tried setting up Jest transformIgnorePatterns, but it does not help.

[lgrammel]

Tests are not run currently.