Mock

A deterministic engine for testing. Replaces the inference step with a predictable local responder — the full agent loop still runs. Tool calls execute, threads accumulate context, stop conditions fire. Everything behaves as in production, just without a model call.

Configuration

import { Mock } from "@axon/engines"

export default defineAgent({
    engine: Mock(),
})

With no argument, Mock() echoes the user's last message back as agent output.

Response patterns

Define fixed responses by pattern:

import { Mock, air } from "@axon/engines"

export default defineAgent({
    engine: Mock({
        "hello": air.text("Hi there!"),
        "run code": air.typescript("math.add(1, 2)"),
    }),
})

Patterns are matched against the user message. On no match, falls back to echo.

For full control, pass a function:

import { Mock, air } from "@axon/engines"

export default defineAgent({
    engine: Mock(async (req) => {
        const last = req.messages.at(-1)?.content ?? ""
        return air.text(`You said: ${last}`)
    }),
})

AIR helpers

Responses must be valid AIR blocks — not plain strings.

Streaming behaviour

Mock streams responses by chunking words with ~5ms delays, matching the feel of a real streaming engine. Tests can iterate the stream normally.