diff --git a/tests/Vantage.App.Tests/OverviewAndAlertWiringTests.cs b/tests/Vantage.App.Tests/OverviewAndAlertWiringTests.cs
new file mode 100644
index 0000000..79281b3
--- /dev/null
+++ b/tests/Vantage.App.Tests/OverviewAndAlertWiringTests.cs
@@ -0,0 +1,132 @@
+using System.Collections.ObjectModel;
+using Vantage.App.ViewModels;
+using Vantage.Core.Alerts;
+using Vantage.Core.Configuration;
+using Vantage.Core.Docker;
+using Vantage.Core.Health;
+using Vantage.Core.History;
+using Vantage.Core.Metrics;
+using Vantage.Core.Models;
+using Xunit;
+
+namespace Vantage.App.Tests;
+
+public class OverviewAndAlertWiringTests
+{
+    private sealed class FixedMetricsProvider : IMetricsProvider
+    {
+        private readonly double cpu;
+
+        public FixedMetricsProvider(double cpu)
+        {
+            this.cpu = cpu;
+        }
+
+        public Task<HostMetrics> GetMetricsAsync(HostConfig host, CancellationToken cancellationToken) =>
+            Task.FromResult(new HostMetrics
+            {
+                CpuUsagePercent = cpu,
+                MemoryUsedBytes = 90,
+                MemoryTotalBytes = 100,
+                DiskUsedBytes = 10,
+                DiskTotalBytes = 100,
+                Load1 = 1,
+                CollectedAt = new DateTimeOffset(2026, 8, 26, 12, 0, 0, TimeSpan.Zero)
+            });
+    }
+
+    private static async Task<IConfigStore> SeededStore(AlertRule rule)
+    {
+        var store = new JsonConfigStore(
+            Path.Combine(Path.GetTempPath(), "vantage-wire-" + Guid.NewGuid().ToString("N"), "config.json"));
+        await store.SaveAsync(new VantageConfig
+        {
+            Hosts = { new HostConfig { Id = "h1", Name = "vps01" } },
+            AlertRules = { rule }
+        });
+        return store;
+    }
+
+    [Fact]
+    public void Overview_AggregatesOnlineOfflineAndPeaks()
+    {
+        var hosts = new ObservableCollection<HostViewModel>
+        {
+            new(new HostConfig { Name = "a" }, 10),
+            new(new HostConfig { Name = "b" }, 10),
+            new(new HostConfig { Name = "c" }, 10)
+        };
+        hosts[0].ApplyMetrics(new HostMetrics { CpuUsagePercent = 20, MemoryTotalBytes = 100, MemoryUsedBytes = 30 });
+        hosts[1].ApplyMetrics(new HostMetrics { CpuUsagePercent = 80, MemoryTotalBytes = 100, MemoryUsedBytes = 60 });
+        hosts[2].ApplyError("down");
+
+        var overview = new OverviewViewModel(hosts);
+        overview.Refresh();
+
+        Assert.Equal(3, overview.TotalHosts);
+        Assert.Equal(2, overview.OnlineHosts);
+        Assert.Equal(1, overview.OfflineHosts);
+        Assert.Equal(50, overview.AverageCpuPercent, 1);
+        Assert.Equal(80, overview.PeakCpuPercent, 1);
+        Assert.Equal("b", overview.PeakCpuHost);
+    }
+
+    [Fact]
+    public async Task Refresh_RecordsHistoryAndFiresAlerts()
+    {
+        await using var store = SqliteMetricsStore.InMemory();
+        var sink = new CollectingSink();
+        var rule = new AlertRule { Name = "CPU", Metric = "cpu", Comparison = AlertComparison.GreaterOrEqual, Threshold = 80, For = TimeSpan.Zero };
+        var engine = new AlertEngine(Array.Empty<AlertRule>(), new IAlertSink[] { sink });
+
+        var viewModel = new MainWindowViewModel(
+            new FixedMetricsProvider(95),
+            new MockDockerProvider(),
+            new HealthChecker(new HttpClient()),
+            await SeededStore(rule),
+            store,
+            engine);
+
+        await viewModel.InitializeAsync();
+        await viewModel.RefreshSelectedHostAsync(CancellationToken.None);
+
+        Assert.True(await store.CountAsync() >= 6);
+        Assert.Contains(sink.Received, n => n.Kind == AlertTransitionKind.Fired);
+        Assert.Equal(1, viewModel.FiringAlertCount);
+        Assert.NotEmpty(viewModel.Alerts);
+    }
+
+    [Fact]
+    public async Task Refresh_BelowThreshold_DoesNotFire()
+    {
+        await using var store = SqliteMetricsStore.InMemory();
+        var sink = new CollectingSink();
+        var rule = new AlertRule { Name = "CPU", Metric = "cpu", Comparison = AlertComparison.GreaterOrEqual, Threshold = 80, For = TimeSpan.Zero };
+        var engine = new AlertEngine(Array.Empty<AlertRule>(), new IAlertSink[] { sink });
+
+        var viewModel = new MainWindowViewModel(
+            new FixedMetricsProvider(15),
+            new MockDockerProvider(),
+            new HealthChecker(new HttpClient()),
+            await SeededStore(rule),
+            store,
+            engine);
+
+        await viewModel.InitializeAsync();
+        await viewModel.RefreshSelectedHostAsync(CancellationToken.None);
+
+        Assert.Empty(sink.Received);
+        Assert.Equal(0, viewModel.FiringAlertCount);
+    }
+
+    private sealed class CollectingSink : IAlertSink
+    {
+        public List<AlertNotification> Received { get; } = new();
+
+        public Task NotifyAsync(AlertNotification notification, CancellationToken cancellationToken = default)
+        {
+            Received.Add(notification);
+            return Task.CompletedTask;
+        }
+    }
+}