feat(voice): add session-scoped mockTools for testing

.changeset/session-scoped-mock-tools.md

@@ -0,0 +1,5 @@
+---
+'@livekit/agents': patch
+---
+
+Add session-scoped `mockTools(agent, mocks, session)` to `voice.testing`: assigns a mock set for an Agent type on a specific session, effective for the session's lifetime. Context-scoped `withMockTools` mocks take precedence when both are active.

agents/src/voice/generation.ts

@@ -1202,7 +1202,7 @@ export function performToolExecutions({
             { functionCall: toolCall, speechHandle },
             async () => {
               const runCtx = new RunContext(session, speechHandle, toolCall);
-              const mock = getMockTool(session.currentAgent, toolCall.name);
+              const mock = getMockTool(session.currentAgent, toolCall.name, session);
               const toolToExecute = mock
                 ? {
                     ...tool,

agents/src/voice/testing/index.ts

@@ -30,6 +30,7 @@ export {
   MessageAssert,
   RunAssert,
   RunResult,
+  mockTools,
   withMockTools,
   type MockToolFn,
   type MockToolsMap,

agents/src/voice/testing/run_result.test.ts

@@ -9,7 +9,7 @@ import { ToolContext, tool } from '../../llm/tool_context.js';
 import { Agent } from '../agent.js';
 import { performToolExecutions } from '../generation.js';
 import { SpeechHandle } from '../speech_handle.js';
-import { activeMockTools, withMockTools } from './run_result.js';
+import { activeMockTools, getMockTool, mockTools, withMockTools } from './run_result.js';
 
 class AgentA extends Agent {
   constructor() {
@@ -180,3 +180,106 @@ describe('withMockTools', () => {
     expect(output.output[0]?.toolCallOutput?.isError).toBe(true);
   });
 });
+
+describe('mockTools (session-scoped)', () => {
+  // mockTools only uses the session as a WeakMap key; a stub is sufficient,
+  // matching the session stubs used by the performToolExecutions tests above.
+  const makeSession = () => ({ currentAgent: undefined }) as never;
+
+  it('registers mocks for a session and resolves them via getMockTool', () => {
+    const session = makeSession();
+    const agent = new AgentA();
+    const mock = () => 'session-mocked';
+
+    mockTools(AgentA, { tool1: mock }, session);
+
+    expect(getMockTool(agent, 'tool1', session)).toBe(mock);
+    // without the session, session-scoped mocks are invisible
+    expect(getMockTool(agent, 'tool1')).toBeUndefined();
+  });
+
+  it('isolates mock sets per session', () => {
+    const sessionA = makeSession();
+    const sessionB = makeSession();
+    const agent = new AgentA();
+
+    mockTools(AgentA, { tool1: () => 'a' }, sessionA);
+
+    expect(getMockTool(agent, 'tool1', sessionA)).toBeDefined();
+    expect(getMockTool(agent, 'tool1', sessionB)).toBeUndefined();
+  });
+
+  it('replaces the mock set on re-registration and removes it with an empty record', () => {
+    const session = makeSession();
+    const agent = new AgentA();
+    const second = () => 'second';
+
+    mockTools(AgentA, { tool1: () => 'first' }, session);
+    mockTools(AgentA, { tool2: second }, session);
+
+    // full replacement: tool1 is gone, tool2 is present
+    expect(getMockTool(agent, 'tool1', session)).toBeUndefined();
+    expect(getMockTool(agent, 'tool2', session)).toBe(second);
+
+    mockTools(AgentA, {}, session);
+    expect(getMockTool(agent, 'tool2', session)).toBeUndefined();
+  });
+
+  it('context-scoped mocks take precedence over session-scoped ones', () => {
+    const session = makeSession();
+    const agent = new AgentA();
+    const sessionMock = () => 'session';
+    const contextMock = () => 'context';
+
+    mockTools(AgentA, { tool1: sessionMock }, session);
+
+    {
+      using _mock = withMockTools(AgentA, { tool1: contextMock });
+      expect(getMockTool(agent, 'tool1', session)).toBe(contextMock);
+    }
+
+    // context scope ended: session mocks apply again
+    expect(getMockTool(agent, 'tool1', session)).toBe(sessionMock);
+  });
+
+  it('routes performToolExecutions to a session-scoped mock', async () => {
+    let realCalled = false;
+    const realTool = tool({
+      name: 'greet',
+      description: 'real',
+      parameters: z.object({ name: z.string() }),
+      execute: async () => {
+        realCalled = true;
+        return 'real';
+      },
+    });
+    const toolCtx = new ToolContext([realTool]);
+    const speechHandle = SpeechHandle.create({ allowInterruptions: false });
+    const session = { currentAgent: new AgentA() } as never;
+
+    mockTools(AgentA, { greet: () => 'session-mocked' }, session);
+
+    const controller = new AbortController();
+    const call = FunctionCall.create({
+      callId: 'call_session_mock',
+      name: 'greet',
+      args: JSON.stringify({ name: 'world' }),
+    });
+    const stream = new ReadableStream<FunctionCall>({
+      start(c) {
+        c.enqueue(call);
+        c.close();
+      },
+    });
+    const [task, output] = performToolExecutions({
+      session,
+      speechHandle,
+      toolCtx,
+      toolCallStream: stream,
+      controller,
+    });
+    await task.result;
+    expect(realCalled).toBe(false);
+    expect(output.output[0]?.rawOutput).toBe('session-mocked');
+  });
+});

agents/src/voice/testing/run_result.ts

@@ -9,6 +9,7 @@ import { tool } from '../../llm/tool_context.js';
 import type { Task } from '../../utils.js';
 import { Future } from '../../utils.js';
 import type { Agent } from '../agent.js';
+import type { AgentSession } from '../agent_session.js';
 import { type SpeechHandle, isSpeechHandle } from '../speech_handle.js';
 import {
   type AgentHandoffAssertOptions,
@@ -966,13 +967,25 @@ export type MockToolsMap = Map<AgentConstructor, Record<string, MockToolFn>>;
 /** @internal */
 export let activeMockTools: MockToolsMap | undefined;
 
-/** @internal */
-export function getMockTool(agent: Agent, toolName: string): MockToolFn | undefined {
-  if (!activeMockTools) return undefined;
+/** @internal – session-scoped mock sets registered via {@link mockTools}. */
+const sessionMockTools = new WeakMap<AgentSession, MockToolsMap>();
 
-  for (const [agentConstructor, mocks] of activeMockTools) {
-    if (agent.constructor === agentConstructor) {
-      return mocks[toolName];
+/** @internal */
+export function getMockTool(
+  agent: Agent,
+  toolName: string,
+  session?: AgentSession,
+): MockToolFn | undefined {
+  // Context-scoped mocks (withMockTools) take precedence over session-scoped
+  // ones (mockTools). A registered mock set fully replaces the tools for its
+  // Agent type — there is no per-tool fallthrough between the two scopes.
+  const scopes = [activeMockTools, session ? sessionMockTools.get(session) : undefined];
+  for (const scope of scopes) {
+    if (!scope) continue;
+    for (const [agentConstructor, mocks] of scope) {
+      if (agent.constructor === agentConstructor) {
+        return mocks[toolName];
+      }
     }
   }
   return undefined;
@@ -1020,6 +1033,42 @@ export function withMockTools(
   };
 }
 
+/**
+ * Assign a set of mock tool callables to a specific Agent type on a session,
+ * effective immediately and for the session's lifetime.
+ *
+ * Mocks intercept tool *execution* only; the LLM keeps seeing the real tool
+ * schemas. Call again to replace the mock set for that Agent type, or pass an
+ * empty record to remove all mocks for it. When both this and
+ * {@link withMockTools} are active, the context-scoped mocks take precedence.
+ *
+ * Mirrors the session form of Python's `mock_tools` (livekit/agents#6080).
+ *
+ * @param agent - The Agent constructor whose tools should be mocked.
+ * @param mocks - A record mapping tool name to a mock implementation.
+ * @param session - The session the mock set is bound to.
+ *
+ * @example
+ * ```typescript
+ * mockTools(DriveThruAgent, { getWeather: () => 'sunny' }, session);
+ *
+ * const result = await session.run({ userInput: "What's the weather?" });
+ * result.expect.containsFunctionCallOutput({ output: 'sunny' });
+ * ```
+ */
+export function mockTools(
+  agent: AgentConstructor,
+  mocks: Record<string, MockToolFn>,
+  session: AgentSession,
+): void {
+  let map = sessionMockTools.get(session);
+  if (!map) {
+    map = new Map();
+    sessionMockTools.set(session, map);
+  }
+  map.set(agent, { ...mocks });
+}
+
 /**
  * Format events for debug output, optionally marking a selected index.
  */