# create_mock_for_function Generate a Jest manual mock file for a specific exported function. 3TG writes the mock to /__mocks__/. per the Jest convention — the path is fixed and not affected by creationMode. Use this when isolating a downstream test from a known dependency. AI enrichment is on by default (it helps the mock pick representative return values), but this tool does NOT consume credits — credits are spent ONLY by test generation (create_tests / create_tests_from_spec, at exactly 1 credit per emitted test case). Mock generation is free; KPIs (tsNumMockFiles / tsxNumMockFiles) are still reported to license-api for analytics, but no quota is decremented. CRITICAL POST-CALL ACTION — write returned files to disk: The MCP server does NOT touch the user's filesystem. It returns the generated file CONTENTS in the response's files array. After this tool returns, you MUST iterate over files and write each entry's content verbatim to its path using your native file-write capability (e.g. Write / edit_file / create_file — whatever your client exposes). Create parent directories as needed. Returned paths are project-root-relative and already translated to the .3tg/ mirror convention where applicable (e.g. specs land under .3tg/.3tg.md; tests / mocks travel through unchanged). Write each path verbatim. Do NOT claim "Generated test file: " unless you have actually written the file. The user will assume the MCP wrote it and waste time looking for a non-existent file. If you can't write for some reason (permission denied, no write capability in this client), return the contents inline in your message so the user can copy-paste them. Never report success silently when the write didn't happen. Agent View of the PolicyLayer registry record for `create_mock_for_function`. HTML page: https://policylayer.com/tools/dev-3tg-mcp/create-mock-for-function ## Facts - Tool: `create_mock_for_function` - Server: 3TG Test Generation (`https://mcp.3tg.dev/mcp`) — https://policylayer.com/tools/dev-3tg-mcp.md - Homepage: https://github.com/https://mcp.3tg.dev/mcp - Risk category: Write (Medium risk) - Registry record: grade D, identity unverified - Server auth posture: open - Server rate-limited: no - Parameters: 7 (4 required) - Recommended policy verdict: Rate-limited ## Parameters | Parameter | Type | Required | Description | | --- | --- | --- | --- | | `clientId` | string | yes | The 3tg.dev client ID. | | `fileName` | string | yes | Path of the source file relative to the user's project root. | | `settings` | object | no | Subset of .3tg/settings.json relevant to this tool. | | `cliConfig` | object | no | Optional per-request 3TG CLI config. The agent assembles this from TWO disk locations and merges them (per-source wins on conflict) before forwarding the merged | | `moduleType` | string | no | Optional Node module type of the consumer project — the value of the `type` field in the project root's `package.json`. The agent reads that one field (only) an | | `sourceCode` | string | yes | Full UTF-8 contents of the source file. | | `functionName` | string | yes | Name of the exported function to mock. Forwarded as `-f `. | Parameters from the server's own tool schema. ## Example call (MCP tools/call, JSON-RPC 2.0) ```json { "jsonrpc": "2.0", "id": 1, "method": "tools/call", "params": { "name": "create_mock_for_function", "arguments": { "clientId": "", "fileName": "", "sourceCode": "", "functionName": "" } } } ``` ## Why create_mock_for_function is rated Medium This tool creates and writes a new file to the project's mock directory structure. While file creation is reversible (files can be deleted), it modifies the project's file system state and could overwrite existing mock files if re-run. This makes it a Write operation rather than Read. From the tool's own definition: "The tool writes a mock file to disk at a fixed path `/__mocks__/.` per Jest convention. The description explicitly states it 'writes the mock' to a specific file system location." Risk signals: Accepts file system path (fileName) · High parameter count (12 properties) · Admin/system-level operation ## Use case AI agents use create_mock_for_function to create or update resources in 3TG Test Generation, usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your 3TG Test Generation environment. ## Recommended policy (PolicyLayer) Verdict: **Rate-limited**. Enforced by the PolicyLayer MCP gateway (https://policylayer.com/mcp-gateway) before a call reaches 3TG Test Generation: ```json { "version": "1", "default": "deny", "tools": { "create_mock_for_function": { "limits": [ { "counter": "create_mock_for_function_rate", "window": "minute", "max": 30, "scope": "grant" } ] } } } ``` ## Other tools on 3TG Test Generation (9) - `get_client_info` — Read — https://policylayer.com/tools/dev-3tg-mcp/get-client-info.md - `help` — Read — https://policylayer.com/tools/dev-3tg-mcp/help.md - `validate_config` — Read — https://policylayer.com/tools/dev-3tg-mcp/validate-config.md - `validate_spec` — Read — https://policylayer.com/tools/dev-3tg-mcp/validate-spec.md - `create_agent_instructions` — Write — https://policylayer.com/tools/dev-3tg-mcp/create-agent-instructions.md - `create_spec` — Write — https://policylayer.com/tools/dev-3tg-mcp/create-spec.md - `create_spec_for_function` — Write — https://policylayer.com/tools/dev-3tg-mcp/create-spec-for-function.md - `create_tests` — Write — https://policylayer.com/tools/dev-3tg-mcp/create-tests.md - `create_tests_from_spec` — Write — https://policylayer.com/tools/dev-3tg-mcp/create-tests-from-spec.md ## For agents This record is a snapshot. Live verdicts and the full registry: - Check every server in your MCP config at once: `npx -y policylayer stack` - Vet a server before you add it: install the mcp-precheck skill — `npx skills add https://policylayer.com` (skill text: https://policylayer.com/skill.md) - Query the registry over MCP: endpoint `https://api.policylayer.com/mcp` — tools `check_mcp_server`, `check_mcp_stack`, `check_tool`, `search_registry`, `get_change_events` --- Source: the PolicyLayer MCP registry — one continuously verified record per MCP server. Full record: https://policylayer.com/registry?q=dev-3tg-mcp · API: https://policylayer.com/registry/api · Policy library: https://policylayer.com/policies/dev-3tg-mcp