Serialize CLI host tests to fix sample_rate race (#17450)

tests/Aspire.Cli.Tests/Telemetry/TelemetryConfigurationTests.cs

@@ -17,6 +17,23 @@ namespace Aspire.Cli.Tests.Telemetry;
 
 public class TelemetryConfigurationTests
 {
+    // The Aspire.Cli.Tests assembly opts out of Azure Monitor telemetry by default
+    // (see TestTelemetryDefaults). Tests that need the Azure Monitor branch override
+    // the env-var-derived opt-out by passing this in their in-memory configuration —
+    // AddInMemoryCollection is added AFTER AddEnvironmentVariables in
+    // Program.BuildApplicationAsync, so the in-memory value wins.
+    private static readonly KeyValuePair<string, string?> s_telemetryOptInOverride =
+        new(AspireCliTelemetry.TelemetryOptOutConfigKey, "false");
+
+    private static Dictionary<string, string?> WithTelemetryOptIn(Dictionary<string, string?>? config = null)
+    {
+        var result = config is null
+            ? new Dictionary<string, string?>()
+            : new Dictionary<string, string?>(config);
+        result[s_telemetryOptInOverride.Key] = s_telemetryOptInOverride.Value;
+        return result;
+    }
+
     private static async Task<IHost> BuildHostAsync(Dictionary<string, string?>? config = null)
     {
         var loggingOptions = Program.ParseLoggingOptions([]);
@@ -30,9 +47,11 @@ private static async Task<IHost> BuildHostAsync(Dictionary<string, string?>? con
     [Fact]
     public async Task AzureMonitor_Enabled_ByDefault()
     {
-        // The Application Insights connection string is now hardcoded, so Azure Monitor
-        // should be enabled by default when telemetry is not opted out
-        using var host = await BuildHostAsync();
+        // The Application Insights connection string is hardcoded, so Azure Monitor
+        // should be enabled when telemetry is not opted out. The test process opts out
+        // by default (see TestTelemetryDefaults); we explicitly opt back in here to
+        // exercise the Azure Monitor branch.
+        using var host = await BuildHostAsync(WithTelemetryOptIn());
 
         var telemetryManager = host.Services.GetService<TelemetryManager>();
         Assert.NotNull(telemetryManager);
@@ -59,10 +78,10 @@ public async Task AzureMonitor_Disabled_WhenOptOutSetToTrueValues(string optOutV
     [Fact]
     public async Task OtlpExporter_WithoutProfiling_EnablesOnlyDebugDiagnostics_WhenEndpointProvided()
     {
-        var config = new Dictionary<string, string?>
+        var config = WithTelemetryOptIn(new Dictionary<string, string?>
         {
             [AspireCliTelemetry.OtlpExporterEndpointConfigKey] = "http://localhost:4317"
-        };
+        });
 
         using var host = await BuildHostAsync(config);
 
@@ -122,11 +141,11 @@ public async Task OtlpExporter_WithProfiling_EnablesProfilingProviderWhenTelemet
     [Fact]
     public async Task OtlpExporter_WithProfiling_KeepsReportedTelemetryAndProfilingSeparate()
     {
-        var config = new Dictionary<string, string?>
+        var config = WithTelemetryOptIn(new Dictionary<string, string?>
         {
             [AspireCliTelemetry.OtlpExporterEndpointConfigKey] = "http://localhost:4317",
             [Aspire.Hosting.KnownConfigNames.ProfilingEnabled] = "true"
-        };
+        });
 
         using var host = await BuildHostAsync(config);
 

tests/Aspire.Cli.Tests/TestTelemetryDefaults.cs

@@ -0,0 +1,33 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Runtime.CompilerServices;
+using Aspire.Cli.Telemetry;
+
+namespace Aspire.Cli.Tests;
+
+/// <summary>
+/// Opts the CLI out of Azure Monitor telemetry for the entire <c>Aspire.Cli.Tests</c>
+/// process. Tests that need to exercise the Azure Monitor branch override this via the
+/// in-memory configuration passed to <see cref="Aspire.Cli.Program.BuildApplicationAsync"/>,
+/// which is layered on top of <c>AddEnvironmentVariables()</c> and therefore wins.
+///
+/// Why opt out by default in tests: see https://github.com/microsoft/aspire/issues/17450.
+/// Azure Monitor's default <c>RateLimitedSampler</c> emits a <c>microsoft.sample_rate</c>
+/// attribute via <c>ActivityCreationOptions.SamplingTags.Add</c> (no <c>TryAdd</c>). When
+/// xUnit v3 runs test classes in parallel and more than one <c>TelemetryManager</c>
+/// builds a TracerProvider in the same process, two listeners are registered on the
+/// <c>Aspire.Cli.Reported</c> ActivitySource and both samplers fire on the same shared
+/// <c>ActivityCreationOptions</c>, so the second <c>Add</c> throws
+/// <c>InvalidOperationException("The collection already contains item with same key 'microsoft.sample_rate'")</c>.
+/// Defaulting the test process to opted-out keeps Azure Monitor out of the pipeline
+/// except in the focused tests that explicitly need it.
+/// </summary>
+internal static class TestTelemetryDefaults
+{
+    [ModuleInitializer]
+    internal static void OptOutByDefault()
+    {
+        Environment.SetEnvironmentVariable(AspireCliTelemetry.TelemetryOptOutConfigKey, "true");
+    }
+}