Teamup/tests/TeamUp.IntegrationTests/McpClientTests.cs

using System.Net;
using System.Net.Http.Json;
using System.Text;
using System.Text.Json;
using TeamUp.Modules.Integrations.Mcp;
using Xunit;

namespace TeamUp.IntegrationTests;

/// <summary>
/// The minimal MCP JSON-RPC client over Streamable HTTP, exercised against a scripted handler: it
/// performs the initialize handshake (capturing the session id), lists tools, and calls a tool —
/// parsing both an application/json reply and a text/event-stream reply.
/// </summary>
public sealed class McpClientTests
{
    [Fact]
    public async Task Lists_tools_and_carries_the_session_id_through_the_handshake()
    {
        var handler = new ScriptedMcpHandler();
        using var http = new HttpClient(handler);
        var client = new McpClient(http);

        var tools = await client.ListToolsAsync("https://mcp.test/mcp", headers: null);

        Assert.Collection(
            tools,
            t => Assert.Equal("search_issues", t.Name),
            t => Assert.Equal("create_issue", t.Name));
        Assert.Equal("Search the issue tracker.", tools[0].Description);

        // initialize → notifications/initialized → tools/list, all after the first reply carrying the session.
        Assert.Equal("initialize", handler.Methods[0]);
        Assert.Equal("notifications/initialized", handler.Methods[1]);
        Assert.Equal("tools/list", handler.Methods[2]);
        Assert.All(handler.SessionIdsAfterInit, id => Assert.Equal("sess-123", id));
    }

    [Fact]
    public async Task Calls_a_tool_and_extracts_text_from_an_sse_reply()
    {
        var handler = new ScriptedMcpHandler();
        using var http = new HttpClient(handler);
        var client = new McpClient(http);

        var (success, content, error) = await client.CallToolAsync(
            "https://mcp.test/mcp", headers: null, toolName: "search_issues", argumentsJson: "{\"q\":\"bug\"}");

        Assert.True(success);
        Assert.Equal("Found 3 issues.", content);
        Assert.Null(error);
        Assert.Equal("tools/call", handler.Methods[^1]);
    }

    /// <summary>Scripts JSON-RPC replies by method; tools/call answers with an SSE-framed body.</summary>
    private sealed class ScriptedMcpHandler : HttpMessageHandler
    {
        public List<string> Methods { get; } = [];

        public List<string?> SessionIdsAfterInit { get; } = [];

        protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
        {
            var body = await request.Content!.ReadFromJsonAsync<JsonElement>(cancellationToken);
            var method = body.GetProperty("method").GetString()!;
            Methods.Add(method);

            if (method != "initialize")
            {
                SessionIdsAfterInit.Add(request.Headers.TryGetValues("Mcp-Session-Id", out var v) ? v.FirstOrDefault() : null);
            }

            // Notifications get a 202 with no body.
            if (!body.TryGetProperty("id", out var idElement))
            {
                return new HttpResponseMessage(HttpStatusCode.Accepted);
            }

            var id = idElement.GetInt32();
            var (payload, sse) = method switch
            {
                "initialize" => (Rpc(id, "{\"protocolVersion\":\"2025-06-18\",\"capabilities\":{}}"), false),
                "tools/list" => (Rpc(id,
                    "{\"tools\":[" +
                    "{\"name\":\"search_issues\",\"description\":\"Search the issue tracker.\",\"inputSchema\":{\"type\":\"object\"}}," +
                    "{\"name\":\"create_issue\",\"description\":\"Open an issue.\",\"inputSchema\":{\"type\":\"object\"}}]}"), false),
                "tools/call" => (Rpc(id, "{\"content\":[{\"type\":\"text\",\"text\":\"Found 3 issues.\"}],\"isError\":false}"), true),
                _ => (Rpc(id, "{}"), false),
            };

            var response = new HttpResponseMessage(HttpStatusCode.OK);
            if (method == "initialize")
            {
                response.Headers.TryAddWithoutValidation("Mcp-Session-Id", "sess-123");
            }

            response.Content = sse
                ? new StringContent("event: message\ndata: " + payload + "\n\n", Encoding.UTF8, "text/event-stream")
                : new StringContent(payload, Encoding.UTF8, "application/json");
            return response;
        }

        private static string Rpc(int id, string resultJson) => "{\"jsonrpc\":\"2.0\",\"id\":" + id + ",\"result\":" + resultJson + "}";
    }
}