Fix debug output clear

src/Adapter/MSTest.CoreAdapter/Execution/LogMessageListener.cs

@@ -96,15 +96,13 @@ public string DebugTrace
 
         public string GetAndClearStandardOutput()
         {
-            var output = this.redirectLoggerOut.ToString();
-            this.redirectLoggerOut.Clear();
+            var output = this.redirectLoggerOut.ToStringAndClear();
             return output;
         }
 
         public string GetAndClearStandardError()
         {
-            var output = this.redirectStdErr.ToString();
-            this.redirectStdErr.Clear();
+            var output = this.redirectStdErr.ToStringAndClear();
             return output;
         }
 
@@ -116,11 +114,9 @@ public string GetAndClearDebugTrace()
                 return null;
             }
 
-            if (writer is StringWriter sw)
+            if (writer is ThreadSafeStringWriter tssw)
             {
-                var sb = sw.GetStringBuilder();
-                var output = sb?.ToString();
-                sb?.Clear();
+                var output = tssw.ToStringAndClear();
                 return output;
             }
 

src/Adapter/PlatformServices.Shared/netstandard1.0/Services/ns10ThreadSafeStringWriter.cs

@@ -51,6 +51,24 @@ public void Clear()
             }
         }
 
+        public string ToStringAndClear()
+        {
+            lock (this.lockObject)
+            {
+                try
+                {
+                    var sb = this.GetStringBuilder();
+                    var output = sb.ToString();
+                    sb.Clear();
+                    return output;
+                }
+                catch (ObjectDisposedException)
+                {
+                    return default(string);
+                }
+            }
+        }
+
         /// <inheritdoc/>
         public override void Write(char value)
         {

src/Adapter/PlatformServices.Shared/netstandard1.3/Services/ns13ThreadSafeStringWriter.cs

@@ -64,11 +64,27 @@ public override string ToString()
             }
         }
 
-        public void Clear()
+        public string ToStringAndClear()
         {
             lock (this.lockObject)
             {
-                this.GetStringBuilderOrNull()?.Clear();
+                try
+                {
+                    var sb = this.GetStringBuilderOrNull();
+
+                    if (sb == null)
+                    {
+                        return default(string);
+                    }
+
+                    var output = sb.ToString();
+                    sb.Clear();
+                    return output;
+                }
+                catch (ObjectDisposedException)
+                {
+                    return default(string);
+                }
             }
         }