Testing

Use nimwire/testing for fast request-level tests. The helpers send the same JSON-RPC shapes the transports dispatch, including the current protocol metadata.

Test a tool call

import std/[json, unittest]
import nimwire
import nimwire/testing

suite "echo server":
  test "returns text":
    let server = mcpServer("test", "1.0.0"):
      server.addTool mcpTool("echo", "Echo text", %*{
        "type": "object",
        "properties": {"text": {"type": "string"}},
        "required": ["text"]
      }, proc (args: JsonNode,
               context: McpContext): McpToolResult =
        textResult(args["text"].getStr))

    let response = server.sendRequest(modernRequest(1, "tools/call", %*{
      "name": "echo",
      "arguments": {"text": "hello"}
    }))

    check response["result"]["resultType"].getStr == "complete"
    check response["result"]["content"][0]["text"].getStr == "hello"

modernRequest adds the JSON-RPC version, the 2026-07-28 protocol version, and empty client capabilities. sendRequest calls the server’s blocking JSON boundary and returns the encoded response.

Assert protocol errors

Send invalid arguments or an unknown method and inspect the error object:

let response = server.sendRequest(modernRequest(2, "tools/call", %*{
  "name": "missing",
  "arguments": {}
}))

check response["error"]["code"].getInt == mcpInvalidParamsCode

Use handleJsonAsync when the test already runs an async event loop.

Test transport behavior

Use newMcpInProcessPeer to exercise request and notification handling through a linked transport:

let peer = newMcpInProcessPeer(server)
let result = peer.request("server/discover")
check result.resultType == mcpComplete
peer.close()

This is useful for composition and message-level behavior. It does not test HTTP headers, CORS, socket disconnects, or stdio framing. Use a local HTTP request adapter or fixture when those boundaries matter.

Related: Transports and the testing API reference.