AgenticCode/tests/ChatAgent.Client.Tests/ChatApiClientTests.cs

using System.Net;
using System.Net.Http.Json;
using System.Text;
using ChatAgent.Client.Services;
using ChatAgent.Shared.Models;

namespace ChatAgent.Client.Tests;

public class ChatApiClientTests
{
    [Fact]
    public async Task SendChatStreamingAsync_ParsesTextDeltas_InOrder()
    {
        // Arrange: build a canned SSE response with two text deltas
        var sse = BuildSSE(
            ("text", "Hello"),
            ("text", " world")
        );

        var handler = new FakeHttpMessageHandler(new HttpResponseMessage(HttpStatusCode.OK)
        {
            Content = new StringContent(sse, Encoding.UTF8, "text/event-stream")
        });

        var httpClient = new HttpClient(handler) { BaseAddress = new Uri("http://localhost") };
        var client = new ChatApiClient(httpClient);

        var request = new ChatRequest
        {
            Messages = new List<ChatMessage>
            {
                new() { Role = "user", Content = "Hi" }
            }
        };

        // Act
        var deltas = new List<string>();
        await foreach (var delta in client.SendChatStreamingAsync(request))
        {
            deltas.Add(delta);
        }

        // Assert
        Assert.Equal(2, deltas.Count);
        Assert.Equal("Hello", deltas[0]);
        Assert.Equal(" world", deltas[1]);
    }

    [Fact]
    public async Task SendChatStreamingAsync_ThrowsOnErrorEvent()
    {
        // Arrange
        var sse = "data: {\"error\":\"Something went wrong\"}\n\n" +
                  "data: [DONE]\n\n";

        var handler = new FakeHttpMessageHandler(new HttpResponseMessage(HttpStatusCode.OK)
        {
            Content = new StringContent(sse, Encoding.UTF8, "text/event-stream")
        });

        var httpClient = new HttpClient(handler) { BaseAddress = new Uri("http://localhost") };
        var client = new ChatApiClient(httpClient);

        var request = new ChatRequest
        {
            Messages = new List<ChatMessage>
            {
                new() { Role = "user", Content = "Hi" }
            }
        };

        // Act & Assert
        var ex = await Assert.ThrowsAsync<HttpRequestException>(async () =>
        {
            await foreach (var _ in client.SendChatStreamingAsync(request))
            {
            }
        });

        Assert.Contains("Something went wrong", ex.Message);
    }

    [Fact]
    public async Task GetHealthAsync_ReturnsHealthResponse()
    {
        // Arrange
        var healthJson = "{\"status\":\"healthy\",\"timestamp\":\"2026-04-04T12:00:00Z\"}";
        var handler = new FakeHttpMessageHandler(new HttpResponseMessage(HttpStatusCode.OK)
        {
            Content = new StringContent(healthJson, Encoding.UTF8, "application/json")
        });

        var httpClient = new HttpClient(handler) { BaseAddress = new Uri("http://localhost") };
        var client = new ChatApiClient(httpClient);

        // Act
        var result = await client.GetHealthAsync();

        // Assert
        Assert.NotNull(result);
        Assert.Equal("healthy", result.Status);
    }

    /// <summary>
    /// Builds simplified SSE content from (type, value) pairs.
    /// Each pair becomes: data: {"text":"value"}\n\n
    /// Ends with data: [DONE]\n\n
    /// </summary>
    private static string BuildSSE(params (string key, string value)[] events)
    {
        var sb = new StringBuilder();
        foreach (var (key, value) in events)
        {
            sb.AppendLine($"data: {{\"{key}\":\"{value}\"}}");
            sb.AppendLine();
        }
        sb.AppendLine("data: [DONE]");
        sb.AppendLine();
        return sb.ToString();
    }
}

/// <summary>
/// Simple fake HttpMessageHandler for unit testing HttpClient-based services.
/// Returns a canned response for any request.
/// </summary>
public class FakeHttpMessageHandler : HttpMessageHandler
{
    private readonly HttpResponseMessage _response;

    public FakeHttpMessageHandler(HttpResponseMessage response)
    {
        _response = response;
    }

    protected override Task<HttpResponseMessage> SendAsync(
        HttpRequestMessage request, CancellationToken cancellationToken)
    {
        return Task.FromResult(_response);
    }
}