fixed paths duplicates

src/Microsoft.TestPlatform.Common/ExtensionFramework/TestPluginCache.cs

@@ -50,7 +50,7 @@ public class TestPluginCache
     /// <summary>
     /// Initializes a new instance of the <see cref="TestPluginCache"/> class.
     /// </summary>
-    protected TestPluginCache()
+    public TestPluginCache()
     {
         _filterableExtensionPaths = new List<string>();
         _unfilterableExtensionPaths = new List<string>();

src/Microsoft.TestPlatform.CrossPlatEngine/DataCollection/InProcDataCollectionExtensionManager.cs

@@ -29,7 +29,7 @@ internal class InProcDataCollectionExtensionManager
 
     private readonly IDataCollectionSink _inProcDataCollectionSink;
     private readonly string? _defaultCodeBase;
-    private readonly List<string?> _codeBasePaths;
+    internal readonly HashSet<string?> CodeBasePaths;
     private readonly IFileHelper _fileHelper;
 
     internal IDictionary<string, IInProcDataCollector> InProcDataCollectors;
@@ -61,13 +61,13 @@ protected InProcDataCollectionExtensionManager(string? runSettings, ITestEventsP
         _inProcDataCollectionSink = new InProcDataCollectionSink();
         _defaultCodeBase = defaultCodeBase;
         _fileHelper = fileHelper;
-        _codeBasePaths = new List<string?> { _defaultCodeBase };
+        CodeBasePaths = new HashSet<string?> { _defaultCodeBase };
 
         // Get Datacollector code base paths from test plugin cache
         var extensionPaths = testPluginCache.GetExtensionPaths(DataCollectorEndsWithPattern);
         foreach (var extensionPath in extensionPaths)
         {
-            _codeBasePaths.Add(Path.GetDirectoryName(extensionPath)!);
+            CodeBasePaths.Add(Path.GetDirectoryName(extensionPath)!);
         }
 
         // Initialize InProcDataCollectors
@@ -248,7 +248,7 @@ private string GetCodebase(string codeBase)
             return codeBase;
         }
 
-        foreach (var extensionPath in _codeBasePaths)
+        foreach (var extensionPath in CodeBasePaths)
         {
             if (extensionPath is null)
             {

test/Microsoft.TestPlatform.CrossPlatEngine.UnitTests/DataCollection/InProcDataCollectionExtensionManagerTests.cs

@@ -53,6 +53,26 @@ public InProcDataCollectionExtensionManagerTests()
         _inProcDataCollectionManager = new TestableInProcDataCollectionExtensionManager(_settingsXml, _mockTestEventsPublisher.Object, _defaultCodebase, _testPluginCache, _mockFileHelper.Object);
     }
 
+    [TestMethod]
+    public void CheckExtensionPathsDuplicates()
+    {
+        var testPluginCache = new TestPluginCache();
+        // the boolean argument refers to adding the paths to which list(we have two lists)and the duplicate happened when we merged the two lists and they had the same path
+        testPluginCache.UpdateExtensions(new List<string> { @"c:\test1\Collector.dll" }, false);
+        testPluginCache.UpdateExtensions(new List<string> { @"c:\test1\Collector.dll", @"c:\test2\Collector.dll" }, true);
+
+        var inProcDataCollectionExtensionManager = new TestableInProcDataCollectionExtensionManager(_settingsXml, _mockTestEventsPublisher.Object, _defaultCodebase, testPluginCache, _mockFileHelper.Object);
+
+        Assert.AreEqual(3, inProcDataCollectionExtensionManager.CodeBasePaths.Count); // "CodeBasePaths" contains the two extensions(after removing duplicates) and the "_defaultCodebase"
+
+        Assert.IsTrue(inProcDataCollectionExtensionManager.CodeBasePaths.Contains(_defaultCodebase));
+        Assert.IsTrue(inProcDataCollectionExtensionManager.CodeBasePaths.Contains(Path.GetDirectoryName(@"c:\test1\Collector.dll")));
+        Assert.IsTrue(inProcDataCollectionExtensionManager.CodeBasePaths.Contains(Path.GetDirectoryName(@"c:\test2\Collector.dll")));
+
+
+    }
+
+
     [TestMethod]
     public void InProcDataCollectionExtensionManagerShouldLoadsDataCollectorsFromRunSettings()
     {