svrnty-mcp-gateway/tests/Svrnty.MCP.Gateway.Infrastructure.Tests/Health/PassiveHealthTrackerTests.cs

using Xunit;
using Svrnty.MCP.Gateway.Infrastructure.Health;
using Svrnty.MCP.Gateway.Core.Models;

namespace Svrnty.MCP.Gateway.Infrastructure.Tests.Health;

/// <summary>
/// Unit tests for PassiveHealthTracker following TDD approach.
/// Tests passive health tracking based on response times and errors.
/// </summary>
public class PassiveHealthTrackerTests
{
    [Fact]
    public void RecordSuccess_UpdatesHealthStatus()
    {
        // Arrange
        var tracker = new PassiveHealthTracker();
        var serverId = "server-1";
        var responseTime = TimeSpan.FromMilliseconds(50);

        // Act
        tracker.RecordSuccess(serverId, responseTime);

        // Assert
        var health = tracker.GetServerHealth(serverId);
        Assert.NotNull(health);
        Assert.True(health.IsHealthy);
        Assert.Equal(responseTime, health.ResponseTime);
    }

    [Fact]
    public void RecordFailure_UpdatesHealthStatus()
    {
        // Arrange
        var tracker = new PassiveHealthTracker
        {
            UnhealthyThreshold = 1 // Mark unhealthy after 1 failure for this test
        };
        var serverId = "server-2";
        var errorMessage = "Connection timeout";

        // Act
        tracker.RecordFailure(serverId, errorMessage);

        // Assert
        var health = tracker.GetServerHealth(serverId);
        Assert.NotNull(health);
        Assert.False(health.IsHealthy);
        Assert.Equal(errorMessage, health.ErrorMessage);
    }

    [Fact]
    public void RecordSuccess_MultipleRequests_CalculatesAverageResponseTime()
    {
        // Arrange
        var tracker = new PassiveHealthTracker();
        var serverId = "server-3";

        // Act - record 3 successful requests
        tracker.RecordSuccess(serverId, TimeSpan.FromMilliseconds(100));
        tracker.RecordSuccess(serverId, TimeSpan.FromMilliseconds(200));
        tracker.RecordSuccess(serverId, TimeSpan.FromMilliseconds(300));

        // Assert
        var health = tracker.GetServerHealth(serverId);
        Assert.NotNull(health);
        Assert.True(health.IsHealthy);
        // Average should be around 200ms
        Assert.NotNull(health.ResponseTime);
        Assert.InRange(health.ResponseTime.Value.TotalMilliseconds, 150, 250);
    }

    [Fact]
    public void RecordFailure_MultipleFailures_MarksServerUnhealthy()
    {
        // Arrange
        var tracker = new PassiveHealthTracker
        {
            UnhealthyThreshold = 3 // Mark unhealthy after 3 failures
        };
        var serverId = "server-4";

        // Act - record 3 failures
        tracker.RecordFailure(serverId, "Error 1");
        tracker.RecordFailure(serverId, "Error 2");
        tracker.RecordFailure(serverId, "Error 3");

        // Assert
        var health = tracker.GetServerHealth(serverId);
        Assert.NotNull(health);
        Assert.False(health.IsHealthy);
    }

    [Fact]
    public void RecordSuccess_AfterFailures_RecoverToHealthy()
    {
        // Arrange
        var tracker = new PassiveHealthTracker
        {
            UnhealthyThreshold = 2,
            HealthyThreshold = 3 // Recover after 3 successes
        };
        var serverId = "server-5";

        // Record failures to make unhealthy
        tracker.RecordFailure(serverId, "Error 1");
        tracker.RecordFailure(serverId, "Error 2");

        // Act - record successes to recover
        tracker.RecordSuccess(serverId, TimeSpan.FromMilliseconds(50));
        tracker.RecordSuccess(serverId, TimeSpan.FromMilliseconds(50));
        tracker.RecordSuccess(serverId, TimeSpan.FromMilliseconds(50));

        // Assert
        var health = tracker.GetServerHealth(serverId);
        Assert.NotNull(health);
        Assert.True(health.IsHealthy);
    }

    [Fact]
    public void GetServerHealth_WithUnknownServer_ReturnsNull()
    {
        // Arrange
        var tracker = new PassiveHealthTracker();

        // Act
        var health = tracker.GetServerHealth("unknown-server");

        // Assert
        Assert.Null(health);
    }

    [Fact]
    public void GetAllServerHealth_ReturnsAllTrackedServers()
    {
        // Arrange
        var tracker = new PassiveHealthTracker
        {
            UnhealthyThreshold = 1 // Mark unhealthy after 1 failure for this test
        };

        tracker.RecordSuccess("server-1", TimeSpan.FromMilliseconds(50));
        tracker.RecordSuccess("server-2", TimeSpan.FromMilliseconds(100));
        tracker.RecordFailure("server-3", "Connection failed");

        // Act
        var allHealth = tracker.GetAllServerHealth();

        // Assert
        Assert.Equal(3, allHealth.Count());
        Assert.Contains(allHealth, h => h.ServerId == "server-1" && h.IsHealthy);
        Assert.Contains(allHealth, h => h.ServerId == "server-2" && h.IsHealthy);
        Assert.Contains(allHealth, h => h.ServerId == "server-3" && !h.IsHealthy);
    }

    [Fact]
    public void RecordSuccess_WithSlowResponse_MarksAsUnhealthy()
    {
        // Arrange
        var tracker = new PassiveHealthTracker
        {
            SlowResponseThreshold = TimeSpan.FromMilliseconds(100)
        };
        var serverId = "server-6";

        // Act - record slow response
        tracker.RecordSuccess(serverId, TimeSpan.FromMilliseconds(500));

        // Assert - should still be marked as success, but noted as slow
        var health = tracker.GetServerHealth(serverId);
        Assert.NotNull(health);
        Assert.True(health.IsHealthy); // Still healthy, just slow
        Assert.Equal(TimeSpan.FromMilliseconds(500), health.ResponseTime);
    }

    [Fact]
    public void Reset_ClearsAllHealthData()
    {
        // Arrange
        var tracker = new PassiveHealthTracker();
        tracker.RecordSuccess("server-1", TimeSpan.FromMilliseconds(50));
        tracker.RecordFailure("server-2", "Error");

        // Act
        tracker.Reset();

        // Assert
        var allHealth = tracker.GetAllServerHealth();
        Assert.Empty(allHealth);
    }

    [Fact]
    public void RecordSuccess_UpdatesLastCheckTime()
    {
        // Arrange
        var tracker = new PassiveHealthTracker();
        var serverId = "server-7";
        var beforeRecord = DateTime.UtcNow;

        // Act
        tracker.RecordSuccess(serverId, TimeSpan.FromMilliseconds(50));
        var afterRecord = DateTime.UtcNow;

        // Assert
        var health = tracker.GetServerHealth(serverId);
        Assert.NotNull(health);
        Assert.True(health.LastCheck >= beforeRecord);
        Assert.True(health.LastCheck <= afterRecord);
    }

    [Fact]
    public void Constructor_SetsDefaultThresholds()
    {
        // Act
        var tracker = new PassiveHealthTracker();

        // Assert
        Assert.Equal(5, tracker.UnhealthyThreshold);
        Assert.Equal(3, tracker.HealthyThreshold);
        Assert.Equal(TimeSpan.FromSeconds(5), tracker.SlowResponseThreshold);
    }
}