Adjusted unit-test to handle isolated TelemetryClient

LOGGING/src/NLogTarget/ApplicationInsightsTarget.cs

@@ -30,7 +30,6 @@ namespace Microsoft.ApplicationInsights.NLogTarget
     public sealed class ApplicationInsightsTarget : TargetWithLayout
     {
         private TelemetryClient telemetryClient;
-        private DateTime lastLogEventTime;
         private NLog.Layouts.Layout instrumentationKeyLayout = string.Empty;
         private NLog.Layouts.Layout connectionStringLayout = string.Empty;
 
@@ -68,12 +67,9 @@ public string ConnectionString
         public IList<TargetPropertyWithContext> ContextProperties { get; } = new List<TargetPropertyWithContext>();
 
         /// <summary>
-        /// Gets the logging controller we will be using.
+        /// Gets or sets the factory for creating TelemetryClient, so unit-tests can assign in-memory-channel.
         /// </summary>
-        internal TelemetryClient TelemetryClient
-        {
-            get { return this.telemetryClient; }
-        }
+        internal Func<TelemetryConfiguration, TelemetryClient> TelemetryClientFactory { get; set; } = new Func<TelemetryConfiguration, TelemetryClient>((cfg) => new TelemetryClient(cfg));
 
         internal void BuildPropertyBag(LogEventInfo logEvent, ITelemetry trace)
         {
@@ -134,7 +130,7 @@ protected override void InitializeTarget()
             {
                 var telemetryConfiguration = TelemetryConfiguration.CreateDefault();
                 telemetryConfiguration.ConnectionString = connectionString;
-                this.telemetryClient = new TelemetryClient(telemetryConfiguration);
+                this.telemetryClient = this.TelemetryClientFactory(telemetryConfiguration);
             }
             else
             {
@@ -162,8 +158,6 @@ protected override void Write(LogEventInfo logEvent)
                 throw new ArgumentNullException(nameof(logEvent));
             }
 
-            this.lastLogEventTime = DateTime.UtcNow;
-
             if (logEvent.Exception != null)
             {
                 this.SendException(logEvent);
@@ -187,7 +181,7 @@ protected override void FlushAsync(AsyncContinuation asyncContinuation)
 
             try
             {
-                this.TelemetryClient.FlushAsync(System.Threading.CancellationToken.None).ContinueWith(t => asyncContinuation(t.Exception));
+                this.telemetryClient.FlushAsync(System.Threading.CancellationToken.None).ContinueWith(t => asyncContinuation(t.Exception));
             }
             catch (Exception ex)
             {

LOGGING/test/NLogTarget.Tests/NLogTargetTests.cs

@@ -565,16 +565,13 @@ private Logger CreateTargetWithGivenConnectionString(
             string connectionString = "Your_ApplicationInsights_ConnectionString",
             Action<Logger> loggerAction = null)
         {
-            // Mock channel to validate that our appender is trying to send logs
-#pragma warning disable CS0618 // Type or member is obsolete
-            TelemetryConfiguration.Active.TelemetryChannel = this.adapterHelper.Channel;
-#pragma warning restore CS0618 // Type or member is obsolete
-
             ApplicationInsightsTarget target = new ApplicationInsightsTarget
             {
                 ConnectionString = connectionString
             };
 
+            target.TelemetryClientFactory = (cfg) => { cfg.TelemetryChannel = this.adapterHelper.Channel; return new TelemetryClient(cfg); };
+
             LoggingRule rule = new LoggingRule("*", LogLevel.Trace, target);
             LoggingConfiguration config = new LoggingConfiguration();
             config.AddTarget("AITarget", target);

LOGGING/test/Shared/AdapterHelper.cs

@@ -19,8 +19,6 @@ public class AdapterHelper : IDisposable
     {
         public string InstrumentationKey { get; }
 
-        public string ConnectionString { get; }
-
 #if NET452 || NET46
         private static readonly string ApplicationInsightsConfigFilePath =
             Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "ApplicationInsights.config");
@@ -29,19 +27,16 @@ public class AdapterHelper : IDisposable
             Path.Combine(Path.GetDirectoryName(typeof(AdapterHelper).GetTypeInfo().Assembly.Location), "ApplicationInsights.config");
 #endif
 
-        public AdapterHelper(string instrumentationKey = "F8474271-D231-45B6-8DD4-D344C309AE69"
-            , string connectionString = "Your_ApplicationInsights_ConnectionString")
+        public AdapterHelper(string instrumentationKey = "F8474271-D231-45B6-8DD4-D344C309AE69")
         {
             this.InstrumentationKey = instrumentationKey;
-            this.ConnectionString = connectionString;
 
             string configuration = string.Format(InvariantCulture,
                                     @"<?xml version=""1.0"" encoding=""utf-8"" ?>
                                      <ApplicationInsights xmlns=""http://schemas.microsoft.com/ApplicationInsights/2013/Settings"">
                                         <InstrumentationKey>{0}</InstrumentationKey>
                                      </ApplicationInsights>",
-                                     instrumentationKey,
-                                     connectionString);
+                                     instrumentationKey);
 
             File.WriteAllText(ApplicationInsightsConfigFilePath, configuration);
             this.Channel = new CustomTelemetryChannel();