Fix safe delete failling windows tests

Author: Christine Zhou

Tst/UnitTests/Runners/PCheckerRunner.cs

@@ -220,6 +220,7 @@ public int RunCheckerInProcess(CheckerConfiguration configuration, string testAs
             {
                 lock (CheckerLock)
                 {
+                    var exitCode = 0;
                     var context = new AssemblyLoadContext($"ALC_{Guid.NewGuid():N}", isCollectible: true);
                     Assembly assembly = context.LoadFromAssemblyPath(testAssemblyPath);
 
@@ -239,14 +240,14 @@ public int RunCheckerInProcess(CheckerConfiguration configuration, string testAs
                     if (bug != null)
                     {
                         stdout += bug;
-                        return 1;
+                        exitCode = 1;
                     }
 
                     context.Unload();
                     GC.Collect();
                     GC.WaitForPendingFinalizers();
 
-                    return 0;
+                    return exitCode;
                 }
             }
             catch (Exception ex)

Tst/UnitTests/TestAssertions.cs

@@ -1,5 +1,6 @@
 using System;
 using System.IO;
+using System.Threading;
 using NUnit.Framework;
 using UnitTests.Core;
 
@@ -33,7 +34,22 @@ public static void SafeDeleteDirectory(DirectoryInfo toDelete)
                 {
                     if (toDelete.Exists)
                     {
-                        toDelete.Delete(true);
+                        for (int i = 0; i < 5; i++)
+                        {
+                            try
+                            {
+                                toDelete.Delete(true);
+                                break;
+                            }
+                            catch (IOException)
+                            {
+                                Thread.Sleep(200);
+                            }
+                            catch (UnauthorizedAccessException)
+                            {
+                                Thread.Sleep(200);
+                            }
+                        }
                     }
 
                     return;