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variable

langchainMatchers: __type

variable

toBeAIMessage: (this: ExpectExtendThis, received: unknown, expected?: string | Record<string, unknown>)

variable

toBeHumanMessage: (this: ExpectExtendThis, received: unknown, expected?: string | Record<string, unknown>)

variable

toBeSystemMessage: (this: ExpectExtendThis, received: unknown, expected?: string | Record<string, unknown>)

variable

toBeToolMessage: (this: ExpectExtendThis, received: unknown, expected?: string | Record<string, unknown>)

Creates a new FakeBuiltModel for testing.

Returns a chainable builder — queue responses, then pass the model anywhere a chat model is expected. Responses are consumed in FIFO order, one per invoke() call.

API summary

Method	Description
`fakeModel()`	Creates a new fake chat model. Returns a chainable builder.
`.respond(message)`	Queue an `AIMessage` (or any `BaseMessage`) to return on the next invocation.
`.respond(error)`	Queue an `Error` to throw on the next invocation.
`.respond(factory)`	Queue a function `(messages) => BaseMessage \\| Error` for dynamic responses.
`.respondWithTools(toolCalls)`	Shorthand for `.respond()` with tool calls. Each entry needs `name` and `args`; `id` is optional.
`.alwaysThrow(error)`	Make every invocation throw this error, regardless of the queue.
`.structuredResponse(value)`	Set the value returned by `.withStructuredOutput()`.
`.bindTools(tools)`	Bind tools to the model. Returns a `RunnableBinding` that shares the response queue and call recording.
`.withStructuredOutput(schema)`	Returns a runnable that produces the `.structuredResponse()` value.
`.calls`	Array of `{ messages, options }` for every invocation (read-only).
`.callCount`	Number of times the model has been invoked.

A fake chat model for testing, created via fakeModel.

Queue responses with .respond() and .respondWithTools(), then pass the instance directly wherever a chat model is expected. Responses are consumed in first-in-first-out order — one per invoke() call. When all queued responses are consumed, further invocations throw.

All matcher functions bundled for convenient use with expect.extend().

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API summary