Tutorial 14

Testing

Demonstrates in-process MCP server testing using the mcptest package — no HTTP, no network.

Demonstrates in-process MCP server testing using the mcptest package — no HTTP, no network.

How It Works

The mcptest package creates a fully wired MCP server in memory. You register tools, resources, prompts, and middleware, then call methods directly:

func TestBasicTool(t *testing.T) {
    ts := mcptest.NewServer(t,
        mcptest.WithTool("greet", func(ctx context.Context, input []byte) ([]byte, error) {
            return []byte("Hello!"), nil
        }, finemcp.WithDescription("Say hello")),
    )
    ts.Initialize(t)
    result := ts.CallTool(t, "greet", nil)
    mcptest.AssertNoError(t, result)
    mcptest.AssertToolResult(t, result, "Hello!")
}

Test Helpers

Function	Description
`mcptest.NewServer(t, opts...)`	Create a test server with tools/resources/prompts
`ts.Initialize(t)`	Initialize the MCP session
`ts.CallTool(t, name, args)`	Call a tool by name
`ts.ListResources(t)`	List registered resources
`ts.ListPrompts(t)`	List registered prompts
`mcptest.AssertNoError(t, result)`	Assert no error in tool result
`mcptest.AssertToolResult(t, result, expected)`	Assert tool returned expected text

Server Options

Option	Description
`mcptest.WithTool(name, handler, opts...)`	Register a raw tool
`mcptest.WithRegisteredTool(tool)`	Register a pre-built tool
`mcptest.WithMiddleware(m)`	Apply middleware
`mcptest.WithResource(resource)`	Register a resource
`mcptest.WithPrompt(prompt)`	Register a prompt

Examples

Testing with Middleware

func TestWithMiddleware(t *testing.T) {
    ts := mcptest.NewServer(t,
        mcptest.WithTool("safe-tool", handler),
        mcptest.WithMiddleware(middleware.Recovery()),
        mcptest.WithMiddleware(middleware.Logging(logger)),
    )
    ts.Initialize(t)
    result := ts.CallTool(t, "safe-tool", nil)
    mcptest.AssertNoError(t, result)
}

Testing Typed Tools

func TestTypedTool(t *testing.T) {
    tool, _ := finemcp.NewTypedTool("add",
        func(ctx context.Context, input struct{ A, B int }) (string, error) {
            return fmt.Sprintf("%d", input.A+input.B), nil
        },
    )
    ts := mcptest.NewServer(t, mcptest.WithRegisteredTool(tool))
    ts.Initialize(t)
    result := ts.CallTool(t, "add", map[string]any{"A": 2, "B": 3})
    mcptest.AssertToolResult(t, result, "5")
}

Running Tests

go test ./14-testing/