diff --git a/src/libraries/Microsoft.Extensions.Diagnostics/tests/MetricsSubscriptionManagerTests.cs b/src/libraries/Microsoft.Extensions.Diagnostics/tests/MetricsSubscriptionManagerTests.cs new file mode 100644 index 00000000000000..60049f6820e963 --- /dev/null +++ b/src/libraries/Microsoft.Extensions.Diagnostics/tests/MetricsSubscriptionManagerTests.cs @@ -0,0 +1,44 @@ +// Licensed to the .NET Foundation under one or more agreements. +// The .NET Foundation licenses this file to you under the MIT license. + +using System; +using System.Collections.Generic; +using System.Diagnostics.Metrics; +using Microsoft.Extensions.DependencyInjection; +using Microsoft.Extensions.Diagnostics.Metrics; +using Microsoft.Extensions.Options; +using Xunit; + +namespace Microsoft.Extensions.Diagnostics.Tests +{ + public class MetricsSubscriptionManagerTests + { + [Fact] + public void AddMetrics_InitializesListeners() + { + var serviceCollection = new ServiceCollection(); + serviceCollection.AddMetrics(); // Duplicate call, should not add things twice. + serviceCollection.AddMetrics(l => l.AddListener()); + var serviceProvider = serviceCollection.BuildServiceProvider(); + + // Make sure the subscription manager is started. + serviceProvider.GetRequiredService().Validate(); + + var listeners = serviceProvider.GetRequiredService>(); + + var listener = Assert.Single(listeners); + var fakeListener = Assert.IsType(listener); + Assert.Equal(1, fakeListener.InitializeCount); + } + + private class FakeListener : IMetricsListener + { + public string Name => "Fake"; + public int InitializeCount { get; private set; } + public MeasurementHandlers GetMeasurementHandlers() => new MeasurementHandlers(); + public void Initialize(IObservableInstrumentsSource source) => InitializeCount++; + public bool InstrumentPublished(Instrument instrument, out object? userState) => throw new NotImplementedException(); + public void MeasurementsCompleted(Instrument instrument, object? userState) => throw new NotImplementedException(); + } + } +}