kotlin-sdk/kotlin-sdk-testing/Module.md

Module kotlin-sdk-testing

kotlin-sdk-testing provides testing utilities for MCP client-server interactions. It eliminates the need for external processes or network connections by offering coroutine-safe in-memory transport implementations that connect clients and servers directly.

Typical usage

1. Create linked transport pair with ChannelTransport.createLinkedPair().
2. Connect client and server concurrently using the paired transports.
3. Configure server request handlers.
4. Execute client operations and verify results.

Complete test example

@OptIn(ExperimentalMcpApi::class)
@Test
fun testClientServerCommunication(): Unit = runBlocking {
    val server = Server(
        Implementation(name = "test server", version = "1.0"),
        ServerOptions(capabilities = ServerCapabilities(resources = ServerCapabilities.Resources())),
    )

    val (clientTransport, serverTransport) = ChannelTransport.createLinkedPair()

    val client = Client(clientInfo = Implementation(name = "test client", version = "1.0"))

    val serverSessionResult = CompletableDeferred<ServerSession>()
    listOf(
        launch { client.connect(clientTransport) },
        launch { serverSessionResult.complete(server.createSession(serverTransport)) },
    ).joinAll()

    val serverSession = serverSessionResult.await()
    serverSession.setRequestHandler<InitializeRequest>(Method.Defined.Initialize) { _, _ ->
        InitializeResult(
            protocolVersion = LATEST_PROTOCOL_VERSION,
            capabilities = ServerCapabilities(
                resources = ServerCapabilities.Resources(null, null),
                tools = ServerCapabilities.Tools(null),
            ),
            serverInfo = Implementation(name = "test", version = "1.0"),
        )
    }

    serverSession.setRequestHandler<ListResourcesRequest>(Method.Defined.ResourcesList) { _, _ ->
        ListResourcesResult(
            resources = listOf(Resource(uri = "/foo/bar", name = "foo-bar-resource")),
        )
    }

    // Test client operations
    client.listResources() shouldNotBeNull {
        this.resources shouldHaveSize 1
    }

    // Clean up resources
    client.close()
    server.close()
}

Note: In production tests, wrap client/server operations in try-finally blocks to ensure proper resource cleanup even if assertions fail.

Use this module for unit and integration testing of MCP implementations without managing external server processes, network ports, or I/O streams. The channel-based transport ensures tests run instantly with full isolation between test cases.