Chore/add tests and update docs

CLAUDE.md

@@ -10,7 +10,7 @@ dotnet test           # Run all tests (multi-targets: net8.0, net9.0, net10.0)
 dotnet test --filter "FullyQualifiedName~SomeTest"  # Run a single test
 ```
 
-Build artifacts go to `/artifacts/bin/` (configured in `Directory.Build.props`).
+Build artifacts go to `/artifacts/bin/` (configured in `Directory.Build.props`). The solution also contains `examples/HealthMonitor.Examples/` with runnable usage examples.
 
 ## Architecture
 
@@ -37,7 +37,9 @@ Build artifacts go to `/artifacts/bin/` (configured in `Directory.Build.props`).
 
 ### DI registration
 
-`AddHealthMonitor()` registers monitors as keyed services (by name, .NET 8+) and via `IEnumerable<IHealthMonitor>` on all targets. The hosted service resolves all monitors through the coordinator.
+`AddHealthMonitor()` registers monitors as keyed services (by name, .NET 8+) and via `IEnumerable<IHealthMonitor>` on all targets. The hosted service resolves all monitors through the coordinator. The call is idempotent for the shared infrastructure (hosted service, coordinator) — call it once per monitor name.
+
+On `netstandard2.0` (no keyed DI), resolve a specific monitor by filtering `IEnumerable<IHealthMonitor>` by `Name`.
 
 ### Dynamic registration (no DI)
 

Directory.Build.props

@@ -1,8 +1,6 @@
 <Project>
   <PropertyGroup>
-    <!-- Redirect all build outputs to a single top-level artifacts directory -->
-    <ArtifactsPath>$(MSBuildThisFileDirectory)artifacts</ArtifactsPath>
-    <!-- Use latest C# regardless of target framework (needed for netstandard2.0) -->
+    <UseArtifactsOutput>true</UseArtifactsOutput>
     <LangVersion>latest</LangVersion>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>

Directory.Packages.props

@@ -7,7 +7,7 @@
     <PackageVersion Include="Microsoft.Extensions.Hosting" Version="8.0.1" />
     <PackageVersion Include="Microsoft.Extensions.Hosting.Abstractions" Version="8.0.1" />
     <PackageVersion Include="Microsoft.Extensions.Logging.Abstractions" Version="8.0.3" />
-    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.4.0" />
+    <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.5.1" />
     <PackageVersion Include="MinVer" Version="7.0.0" />
     <PackageVersion Include="Serilog.Extensions.Hosting" Version="8.0.0" />
     <PackageVersion Include="Serilog.Sinks.Console" Version="6.1.1" />

README.md

@@ -3,6 +3,7 @@
 [![CI](https://github.com/coldhighsun/HealthMonitor/actions/workflows/ci.yml/badge.svg)](https://github.com/coldhighsun/HealthMonitor/actions/workflows/ci.yml)
 [![NuGet Version](https://img.shields.io/nuget/v/HealthMonitor.Core)](https://www.nuget.org/packages/HealthMonitor.Core)
 [![NuGet Downloads](https://img.shields.io/nuget/dt/HealthMonitor.Core)](https://www.nuget.org/packages/HealthMonitor.Core)
+[![License: MIT](https://img.shields.io/badge/License-MIT-blue.svg)](LICENSE)
 
 A lightweight .NET library for monitoring application health via periodic heartbeats. Supports dependency injection, multiple named monitors, and fires `Degraded` / `Recovered` events on state transitions.
 
@@ -120,7 +121,7 @@ monitor.Signal();
 ```csharp
 using var manager = new DynamicHealthMonitorManager();
 
-// Subscribe once on the manager — fires for all monitors, including those added later
+// Subscribe at any time — fires for all registered monitors, regardless of when they were added
 manager.Degraded  += (_, e) => Console.WriteLine($"{e.MonitorName} degraded");
 manager.Recovered += (_, e) => Console.WriteLine($"{e.MonitorName} recovered");
 
@@ -178,6 +179,7 @@ Build outputs land in `./artifacts/bin/`.
 [![CI](https://github.com/coldhighsun/HealthMonitor/actions/workflows/ci.yml/badge.svg)](https://github.com/coldhighsun/HealthMonitor/actions/workflows/ci.yml)
 [![NuGet 版本](https://img.shields.io/nuget/v/HealthMonitor.Core)](https://www.nuget.org/packages/HealthMonitor.Core)
 [![NuGet 下载量](https://img.shields.io/nuget/dt/HealthMonitor.Core)](https://www.nuget.org/packages/HealthMonitor.Core)
+[![License: MIT](https://img.shields.io/badge/License-MIT-blue.svg)](LICENSE)
 
 轻量级 .NET 健康监控库，通过周期性心跳信号判断组件是否存活，在状态切换时触发 `Degraded` / `Recovered` 事件。支持依赖注入、多个命名监控器。
 
@@ -295,7 +297,7 @@ monitor.Signal();
 ```csharp
 using var manager = new DynamicHealthMonitorManager();
 
-// 在 manager 上订阅一次 — 对所有监控器生效，包括后续动态添加的
+// 可在任意时机订阅 — 对所有已注册的监控器生效，无论添加顺序
 manager.Degraded  += (_, e) => Console.WriteLine($"{e.MonitorName} 已降级");
 manager.Recovered += (_, e) => Console.WriteLine($"{e.MonitorName} 已恢复");
 

tests/HealthMonitor.Tests/Monitors/DynamicHealthMonitorManagerTests.cs

@@ -299,6 +299,27 @@ public void TryGet_NonExistentMonitor_ReturnsNull()
         Assert.Null(manager.TryGet("missing"));
     }
 
+    [Fact]
+    public async Task ManagerDegraded_FiresForHandlerSubscribedAfterAdd()
+    {
+        using var manager = new DynamicHealthMonitorManager(new FakeSystemTimeProvider());
+
+        manager.Add("svc", new HealthMonitorOptions
+        {
+            DegradedThreshold = TimeSpan.FromMilliseconds(100),
+            CheckInterval = TimeSpan.FromMilliseconds(50),
+        });
+
+        // Subscribe AFTER adding the monitor
+        HealthDegradedEventArgs? captured = null;
+        manager.Degraded += (_, e) => captured = e;
+
+        await PollUntil(() => captured is not null, timeout: TimeSpan.FromSeconds(5));
+
+        Assert.NotNull(captured);
+        Assert.Equal("svc", captured.MonitorName);
+    }
+
     private static async Task PollUntil(Func<bool> condition, TimeSpan timeout)
     {
         var deadline = DateTime.UtcNow + timeout;

tests/HealthMonitor.Tests/Monitors/HealthMonitorBaseTests.cs

@@ -218,6 +218,56 @@ private static (
         return (monitor, clock, signalWatch, checkWatch, stateWatch);
     }
 
+    [Fact]
+    public void Recovered_Args_Timestamp_UsesWallClock()
+    {
+        var (monitor, clock, signalWatch, checkWatch, _) = CreateMonitor();
+
+        // Degrade first
+        signalWatch.Advance(TimeSpan.FromSeconds(31));
+        checkWatch.Advance(TimeSpan.FromSeconds(5));
+        monitor.Tick();
+
+        HealthRecoveredEventArgs? recovered = null;
+        ((IHealthMonitor)monitor).Recovered += (_, e) => recovered = e;
+
+        clock.Advance(TimeSpan.FromMinutes(1));
+        var expectedTime = clock.UtcNow;
+        ((IHealthMonitor)monitor).Signal();
+
+        Assert.NotNull(recovered);
+        Assert.Equal(expectedTime, recovered.Timestamp);
+    }
+
+    [Fact]
+    public void Degrade_Recover_Degrade_CycleWorks()
+    {
+        var (monitor, _, signalWatch, checkWatch, _) = CreateMonitor(degradedThreshold: TimeSpan.FromSeconds(30));
+
+        var degradedCount = 0;
+        var recoveredCount = 0;
+        ((IHealthMonitor)monitor).Degraded += (_, _) => degradedCount++;
+        ((IHealthMonitor)monitor).Recovered += (_, _) => recoveredCount++;
+
+        // First degradation
+        signalWatch.Advance(TimeSpan.FromSeconds(31));
+        checkWatch.Advance(TimeSpan.FromSeconds(5));
+        monitor.Tick();
+        Assert.Equal(1, degradedCount);
+
+        // Recovery
+        ((IHealthMonitor)monitor).Signal();
+        Assert.Equal(1, recoveredCount);
+        Assert.True(monitor.IsHealthy);
+
+        // Second degradation
+        signalWatch.Advance(TimeSpan.FromSeconds(31));
+        checkWatch.Advance(TimeSpan.FromSeconds(5));
+        monitor.Tick();
+        Assert.Equal(2, degradedCount);
+        Assert.False(monitor.IsHealthy);
+    }
+
     // ── Initial state ──────────────────────────────────────────────────────────
     // ── Degraded ───────────────────────────────────────────────────────────────
     // ── Signal / Recovered ─────────────────────────────────────────────────────

tests/HealthMonitor.Tests/Services/DependencyInjectionTests.cs

@@ -86,6 +86,22 @@ public void AddHealthMonitor_RegistersSingleMonitor()
         Assert.Equal("quotes", monitors[0].Name);
     }
 
+    [Fact]
+    public void AddHealthMonitor_IsIdempotent_ForSharedInfrastructure()
+    {
+        using var provider = BuildProvider(s =>
+        {
+            s.AddHealthMonitor("quotes");
+            s.AddHealthMonitor("orders");
+        });
+
+        // Shared infrastructure (hosted service) should be registered exactly once
+        var hostedServices = provider.GetRequiredService<IEnumerable<IHostedService>>()
+            .Where(hs => hs.GetType().Name == "HealthMonitorHostedService")
+            .ToList();
+        Assert.Single(hostedServices);
+    }
+
     private static ServiceProvider BuildProvider(Action<IServiceCollection> configure)
     {
         var services = new ServiceCollection();