Write a programmatic TypeScript MCP client / automated test harness (connect, listTools, callTool)

Documented steps

1. Install the separate client package: npm install @modelcontextprotocol/client. Docs: https://raw.githubusercontent.com/modelcontextprotocol/typescript-sdk/main/docs/get-started/first-client.md
2. Stdio client: import { Client } from '@modelcontextprotocol/client' and { StdioClientTransport } from '@modelcontextprotocol/client/stdio'; const client = new Client({ name: 'harness', version: '1.0.0' }); await client.connect(new StdioClientTransport({ command: 'npx', args: ['tsx', 'src/index.ts'] })); — connect() spawns the server child process itself and runs the handshake.
3. List tools: const { tools } = await client.listTools(); each tool's inputSchema is plain JSON Schema, ready to pass to any tool-calling LLM API unchanged.
4. Call a tool: const result = await client.callTool({ name: 'get-alerts', arguments: { state: 'CA' } }); iterate result.content blocks (type 'text' etc.).
5. For in-process tests of HTTP-mode servers (no network, no subprocess): const handler = createMcpHandler(createServer); const transport = new StreamableHTTPClientTransport(new URL('http://test.local/mcp'), { fetch: (url, init) => handler.fetch(new Request(url, init)) }); — pass handler.fetch as the client transport's fetch option. See https://raw.githubusercontent.com/modelcontextprotocol/typescript-sdk/main/docs/testing.md
6. Assert on structured output: const r = await client.callTool({ name: 'apply-discount', arguments: { price: 80, percent: 25 } }); assert.deepStrictEqual(r.structuredContent, { total: 60 }); teardown with await client.close(); await handler.close();
7. Pure in-memory pairing without HTTP: const [clientTransport, serverTransport] = InMemoryTransport.createLinkedPair(); await server.connect(serverTransport); await client.connect(clientTransport); — the two transports are each other's wire.