Testing

The AITesting library is the ai/test analog: deterministic doubles for your test targets, no network, no keys. Add the product next to AI:

Package.swift

.testTarget(
  name: "MyAppTests",
  dependencies: [
    .product(name: "AI", package: "swift-ai-sdk"),
    .product(name: "AITesting", package: "swift-ai-sdk")
  ]
)

MockLanguageModel

The one-liner covers most tests:

import AITesting

func testGreeting() async throws {
  let model = MockLanguageModel(text: "Hello, world!")
  let result = try await generateText(model: model, prompt: "Hi")
  XCTAssertEqual(result.text, "Hello, world!")
}

Every request is recorded, so you can assert on exactly what your code sent:

XCTAssertEqual(model.requests.count, 1)
XCTAssertEqual(model.requests[0].messages.last?.text, "Hi")
XCTAssertEqual(model.requests[0].reasoning, .medium)

Scripting multi-step loops

responses: provides one part-array per model round-trip; calls past the end replay the last script. That is enough to test a full tool loop:

let model = MockLanguageModel(responses: [
  [
    .toolCall(ToolCall(id: "c1", name: "search", arguments: ["q": "swift"])),
    .finish(reason: .toolCalls, usage: .init())
  ],
  [
    .textDelta("Found it."),
    .finish(reason: .stop, usage: .init())
  ]
])

let result = try await generateText(model: model, prompt: "go", tools: [searchTool])
XCTAssertEqual(result.stepCount, 2)
XCTAssertEqual(result.text, "Found it.")

For full control, compute parts from the request and call number:

let model = MockLanguageModel { request, callIndex in
  [.textDelta("call #\(callIndex)"), .finish(reason: .stop, usage: .init())]
}

Pass chunkDelay: to pace parts like a live stream.

MockEmbeddingModel

let model = MockEmbeddingModel(vectors: [[1, 0], [0, 1]])
let result = try await embedMany(model: model, values: ["a", "b", "c"])
// vectors cycle; model.batches records every input batch

Stream and value helpers

// Any chunk array as a paced AsyncThrowingStream: test UI pipelines
// without a model at all.
let chunks = simulateReadableStream(
  chunks: uiMessageChunks,
  initialDelay: .milliseconds(100),
  chunkDelay: .milliseconds(10)
)

// Deterministic id generators: hands out values in order, sticks at the last.
let nextID = mockValues("id-1", "id-2", "id-3")

Testing chat UIs

Sessions take transports, and an Agent over a mock model is a transport, so a full ChatSession test needs no HTTP:

let agent = Agent(model: MockLanguageModel(text: "Hi there!"))
let chat = ChatSession(transport: agent)
chat.send("Hello")
// await chat.status == .ready, then assert on chat.messages