How to Verify that an OpenTelemetry Trace is produced in a unit test

verify-opentelemetry-trace.cs

    [Fact]
    public async Task InterceptShouldTrace()
    {
        IList<Activity> exportedActivities = new List<Activity>();
        
        IHostBuilder hostBuilder = Host.CreateDefaultBuilder();

        var source = Guid.NewGuid().ToString("N");
        
        hostBuilder.ConfigureServices((_, serviceCollection) =>
        {
            serviceCollection.AddOpenTelemetry()
                .WithTracing(builder =>
                {
                    builder.AddSource(source);
                    builder.AddInMemoryExporter(exportedActivities);
                });
            
            serviceCollection.AddSingleton(TracerProvider.Default.GetTracer(source));
        });

        IHost host = hostBuilder.Build();
        await host.StartAsync();
        var tracer = ActivatorUtilities.GetServiceOrCreateInstance<Tracer>(host.Services);

        var tracingInterceptor = new TracingInterceptor(tracer);
        
        var interceptInvocation = Mock.Of<IInvocation>(invocation =>
            invocation.TargetType == typeof(MyTraceTarget) && 
            invocation.Method == typeof(MyTraceTarget).GetMethod(nameof(MyTraceTarget.GetSomething)));

        tracingInterceptor.Intercept(interceptInvocation);

        exportedActivities.Should().Contain(activity => activity.OperationName == $"{nameof(MyTraceTarget)}.{nameof(MyTraceTarget.GetSomething)}" && activity.TagObjects.Any(pair => pair.Key == "injected"));

        await host.StopAsync();
    }