Make the log file name unique per session (#50)

* Make the log file name unique per session

* Try to use PID for unique ID

test/Microsoft.SqlTools.ServiceLayer.Test/ServiceHost/LoggerTests.cs

@@ -0,0 +1,62 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+using System.IO;
+using System.Linq;
+using Microsoft.SqlTools.EditorServices.Utility;
+using Xunit;
+
+namespace Microsoft.SqlTools.ServiceLayer.Test.ServiceHost
+{
+    /// <summary>
+    /// Logger test cases
+    /// </summary>
+    public class LoggerTests
+    {
+       
+        /// <summary>
+        /// Test to verify that the logger initialization is generating a valid file
+        /// </summary>
+        [Fact]
+        public void LoggerDefaultFile()
+        {
+            // delete any existing log files from the current directory 
+            Directory.GetFiles(Directory.GetCurrentDirectory())
+                .Where(fileName 
+                     => fileName.Contains("sqltools_") 
+                     && fileName.EndsWith(".log", StringComparison.OrdinalIgnoreCase))
+                .ToList()
+                .ForEach(fileName => File.Delete(fileName));
+
+            // initialize the logger
+            Logger.Initialize(
+                logFilePath: Path.Combine(Directory.GetCurrentDirectory(), "sqltools"),
+                minimumLogLevel: LogLevel.Verbose);
+
+            // close the logger
+            Logger.Close();
+
+            // find the name of the new log file
+            string logFileName = Directory.GetFiles(Directory.GetCurrentDirectory())
+                .Where(fileName 
+                     => fileName.Contains("sqltools_") 
+                     && fileName.EndsWith(".log", StringComparison.OrdinalIgnoreCase)).SingleOrDefault();
+                
+            // validate the log file was created with desired name 
+            Assert.True(!string.IsNullOrWhiteSpace(logFileName));
+            if (!string.IsNullOrWhiteSpace(logFileName))
+            {
+                Assert.True(logFileName.Length > "sqltools_.log".Length);
+                Assert.True(File.Exists(logFileName));
+
+                // delete the test log file
+                if (File.Exists(logFileName))
+                {
+                    File.Delete(logFileName);
+                }
+            }
+        }
+    }
+}