Refactor `ImportDocumentManager` to not be windows specific.

- Added a `FileChangeTracker`, `FileChangeTrackerFactory` and corresponding implementations. These types now enable us to implement Windows and Mac file change tracking instead of replacing the entire import manager.
- Changed the import manager to be a Roslyn based service.
- Moved import manager implementation to the editor.razor assembly now since it no longer depends on windows.
- Updated import manager unit tests.
- Added import manager integration test
- Added file change tracking tests.

#1804

src/Microsoft.VisualStudio.Editor.Razor/DefaultImportDocumentManager.cs

@@ -0,0 +1,162 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.IO;
+using Microsoft.AspNetCore.Razor.Language;
+using Microsoft.CodeAnalysis.Razor;
+
+namespace Microsoft.VisualStudio.Editor.Razor
+{
+    internal class DefaultImportDocumentManager : ImportDocumentManager
+    {
+        private readonly FileChangeTrackerFactory _fileChangeTrackerFactory;
+        private readonly ForegroundDispatcher _foregroundDispatcher;
+        private readonly ErrorReporter _errorReporter;
+        private readonly RazorTemplateEngineFactoryService _templateEngineFactoryService;
+        private readonly Dictionary<string, ImportTracker> _importTrackerCache;
+
+        public override event EventHandler<ImportChangedEventArgs> Changed;
+
+        public DefaultImportDocumentManager(
+            ForegroundDispatcher foregroundDispatcher,
+            ErrorReporter errorReporter,
+            FileChangeTrackerFactory fileChangeTrackerFactory,
+            RazorTemplateEngineFactoryService templateEngineFactoryService)
+        {
+            if (foregroundDispatcher == null)
+            {
+                throw new ArgumentNullException(nameof(foregroundDispatcher));
+            }
+
+            if (errorReporter == null)
+            {
+                throw new ArgumentNullException(nameof(errorReporter));
+            }
+
+            if (fileChangeTrackerFactory == null)
+            {
+                throw new ArgumentNullException(nameof(fileChangeTrackerFactory));
+            }
+
+            if (templateEngineFactoryService == null)
+            {
+                throw new ArgumentNullException(nameof(templateEngineFactoryService));
+            }
+
+            _foregroundDispatcher = foregroundDispatcher;
+            _errorReporter = errorReporter;
+            _fileChangeTrackerFactory = fileChangeTrackerFactory;
+            _templateEngineFactoryService = templateEngineFactoryService;
+            _importTrackerCache = new Dictionary<string, ImportTracker>(StringComparer.OrdinalIgnoreCase);
+        }
+
+        public override void OnSubscribed(VisualStudioDocumentTracker tracker)
+        {
+            if (tracker == null)
+            {
+                throw new ArgumentNullException(nameof(tracker));
+            }
+
+            _foregroundDispatcher.AssertForegroundThread();
+
+            var imports = GetImportItems(tracker);
+            foreach (var import in imports)
+            {
+                var importFilePath = import.PhysicalPath;
+                Debug.Assert(importFilePath != null);
+
+                if (!_importTrackerCache.TryGetValue(importFilePath, out var importTracker))
+                {
+                    // First time seeing this import. Start tracking it.
+                    var fileChangeTracker = _fileChangeTrackerFactory.Create(importFilePath);
+                    importTracker = new ImportTracker(fileChangeTracker);
+                    _importTrackerCache[importFilePath] = importTracker;
+
+                    fileChangeTracker.Changed += FileChangeTracker_Changed;
+                    fileChangeTracker.StartListening();
+                }
+
+                importTracker.AssociatedDocuments.Add(tracker.FilePath);
+            }
+        }
+
+        public override void OnUnsubscribed(VisualStudioDocumentTracker tracker)
+        {
+            if (tracker == null)
+            {
+                throw new ArgumentNullException(nameof(tracker));
+            }
+
+            _foregroundDispatcher.AssertForegroundThread();
+
+            var imports = GetImportItems(tracker);
+            foreach (var import in imports)
+            {
+                var importFilePath = import.PhysicalPath;
+                Debug.Assert(importFilePath != null);
+
+                if (_importTrackerCache.TryGetValue(importFilePath, out var importTracker))
+                {
+                    importTracker.AssociatedDocuments.Remove(tracker.FilePath);
+
+                    if (importTracker.AssociatedDocuments.Count == 0)
+                    {
+                        // There are no open documents that care about this import. We no longer need to track it.
+                        importTracker.FileChangeTracker.StopListening();
+                        _importTrackerCache.Remove(importFilePath);
+                    }
+                }
+            }
+        }
+
+        private IEnumerable<RazorProjectItem> GetImportItems(VisualStudioDocumentTracker tracker)
+        {
+            var projectDirectory = Path.GetDirectoryName(tracker.ProjectPath);
+            var templateEngine = _templateEngineFactoryService.Create(projectDirectory, _ => { });
+            var imports = templateEngine.GetImportItems(tracker.FilePath);
+
+            return imports;
+        }
+
+        private void OnChanged(ImportTracker importTracker, FileChangeKind changeKind)
+        {
+            _foregroundDispatcher.AssertForegroundThread();
+
+            if (Changed == null)
+            {
+                return;
+            }
+
+            var args = new ImportChangedEventArgs(importTracker.FilePath, changeKind, importTracker.AssociatedDocuments);
+            Changed.Invoke(this, args);
+    }
+
+        private void FileChangeTracker_Changed(object sender, FileChangeEventArgs args)
+        {
+            _foregroundDispatcher.AssertForegroundThread();
+
+            if (_importTrackerCache.TryGetValue(args.FilePath, out var importTracker))
+            {
+                OnChanged(importTracker, args.Kind);
+            }
+        }
+
+        private class ImportTracker
+        {
+            public ImportTracker(FileChangeTracker fileChangeTracker)
+            {
+                FileChangeTracker = fileChangeTracker;
+                AssociatedDocuments = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
+            }
+
+            public string FilePath => FileChangeTracker.FilePath;
+
+            public FileChangeTracker FileChangeTracker { get; }
+
+            public HashSet<string> AssociatedDocuments { get; }
+        }
+    }
+}

src/Microsoft.VisualStudio.Editor.Razor/DefaultImportDocumentManagerFactory.cs

@@ -0,0 +1,35 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using System.Composition;
+using Microsoft.CodeAnalysis.Host;
+using Microsoft.CodeAnalysis.Host.Mef;
+using Microsoft.CodeAnalysis.Razor;
+
+namespace Microsoft.VisualStudio.Editor.Razor
+{
+    [Shared]
+    [ExportLanguageServiceFactory(typeof(ImportDocumentManager), RazorLanguage.Name, ServiceLayer.Default)]
+    internal class DefaultImportDocumentManagerFactory : ILanguageServiceFactory
+    {
+        public ILanguageService CreateLanguageService(HostLanguageServices languageServices)
+        {
+            if (languageServices == null)
+            {
+                throw new ArgumentNullException(nameof(languageServices));
+            }
+
+            var dispatcher = languageServices.WorkspaceServices.GetRequiredService<ForegroundDispatcher>();
+            var errorReporter = languageServices.WorkspaceServices.GetRequiredService<ErrorReporter>();
+            var fileChangeTrackerFactory = languageServices.GetRequiredService<FileChangeTrackerFactory>();
+            var templateEngineFactoryService = languageServices.GetRequiredService<RazorTemplateEngineFactoryService>();
+
+            return new DefaultImportDocumentManager(
+                dispatcher,
+                errorReporter,
+                fileChangeTrackerFactory,
+                templateEngineFactoryService);
+        }
+    }
+}

src/Microsoft.VisualStudio.Editor.Razor/DefaultVisualStudioDocumentTrackerFactoryFactory.cs

@@ -18,13 +18,11 @@ namespace Microsoft.VisualStudio.Editor.Razor
     {
         private readonly TextBufferProjectService _projectService;
         private readonly ITextDocumentFactoryService _textDocumentFactory;
-        private readonly ImportDocumentManager _importDocumentManager;
 
         [ImportingConstructor]
         public DefaultVisualStudioDocumentTrackerFactoryFactory(
             TextBufferProjectService projectService,
-            ITextDocumentFactoryService textDocumentFactory,
+            ITextDocumentFactoryService textDocumentFactory)
-            ImportDocumentManager importDocumentManager)
         {
             if (projectService == null)
             {
@@ -36,14 +34,8 @@ namespace Microsoft.VisualStudio.Editor.Razor
                 throw new ArgumentNullException(nameof(textDocumentFactory));
             }
 
-            if (importDocumentManager == null)
-            {
-                throw new ArgumentNullException(nameof(importDocumentManager));
-            }
-
             _projectService = projectService;
             _textDocumentFactory = textDocumentFactory;
-            _importDocumentManager = importDocumentManager;
         }
 
         public ILanguageService CreateLanguageService(HostLanguageServices languageServices)
@@ -56,6 +48,7 @@ namespace Microsoft.VisualStudio.Editor.Razor
             var dispatcher = languageServices.WorkspaceServices.GetRequiredService<ForegroundDispatcher>();
             var projectManager = languageServices.GetRequiredService<ProjectSnapshotManager>();
             var editorSettingsManager = languageServices.GetRequiredService<EditorSettingsManagerInternal>();
+            var importDocumentManager = languageServices.GetRequiredService<ImportDocumentManager>();
 
             return new DefaultVisualStudioDocumentTrackerFactory(
                 dispatcher,
@@ -63,7 +56,7 @@ namespace Microsoft.VisualStudio.Editor.Razor
                 editorSettingsManager,
                 _projectService,
                 _textDocumentFactory,
-                _importDocumentManager,
+                importDocumentManager,
                 languageServices.WorkspaceServices.Workspace);
         }
     }

src/Microsoft.VisualStudio.Editor.Razor/FileChangeEventArgs.cs

@@ -0,0 +1,20 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+
+namespace Microsoft.VisualStudio.Editor.Razor
+{
+    internal sealed class FileChangeEventArgs : EventArgs
+    {
+        public FileChangeEventArgs(string filePath, FileChangeKind kind)
+        {
+            FilePath = filePath;
+            Kind = kind;
+        }
+
+        public string FilePath { get; }
+
+        public FileChangeKind Kind { get; }
+    }
+}

src/Microsoft.VisualStudio.Editor.Razor/FileChangeKind.cs

@@ -3,7 +3,7 @@
 
 namespace Microsoft.VisualStudio.Editor.Razor
 {
-    internal enum ImportChangeKind
+    internal enum FileChangeKind
     {
         Added,
         Removed,

src/Microsoft.VisualStudio.Editor.Razor/FileChangeTracker.cs

@@ -0,0 +1,18 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+
+namespace Microsoft.VisualStudio.Editor.Razor
+{
+    internal abstract class FileChangeTracker
+    {
+        public abstract event EventHandler<FileChangeEventArgs> Changed;
+
+        public abstract string FilePath { get; }
+
+        public abstract void StartListening();
+
+        public abstract void StopListening();
+    }
+}

src/Microsoft.VisualStudio.Editor.Razor/FileChangeTrackerFactory.cs

@@ -0,0 +1,12 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using Microsoft.CodeAnalysis.Host;
+
+namespace Microsoft.VisualStudio.Editor.Razor
+{
+    internal abstract class FileChangeTrackerFactory : ILanguageService
+    {
+        public abstract FileChangeTracker Create(string filePath);
+    }
+}

src/Microsoft.VisualStudio.Editor.Razor/ImportChangedEventArgs.cs

@@ -8,7 +8,7 @@ namespace Microsoft.VisualStudio.Editor.Razor
 {
     internal class ImportChangedEventArgs : EventArgs
     {
-        public ImportChangedEventArgs(string filePath, ImportChangeKind kind, IEnumerable<string> associatedDocuments)
+        public ImportChangedEventArgs(string filePath, FileChangeKind kind, IEnumerable<string> associatedDocuments)
         {
             FilePath = filePath;
             Kind = kind;
@@ -17,7 +17,7 @@ namespace Microsoft.VisualStudio.Editor.Razor
 
         public string FilePath { get; }
 
-        public ImportChangeKind Kind { get; }
+        public FileChangeKind Kind { get; }
 
         public IEnumerable<string> AssociatedDocuments { get; }
     }

src/Microsoft.VisualStudio.Editor.Razor/ImportDocumentManager.cs

@@ -2,10 +2,11 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using Microsoft.CodeAnalysis.Host;
 
 namespace Microsoft.VisualStudio.Editor.Razor
 {
-    internal abstract class ImportDocumentManager
+    internal abstract class ImportDocumentManager : ILanguageService
     {
         public abstract event EventHandler<ImportChangedEventArgs> Changed;
 

src/Microsoft.VisualStudio.LanguageServices.Razor/DefaultFileChangeTracker.cs

@@ -0,0 +1,141 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using System.Diagnostics;
+using System.Runtime.InteropServices;
+using Microsoft.CodeAnalysis.Razor;
+using Microsoft.VisualStudio.Editor.Razor;
+using Microsoft.VisualStudio.Shell.Interop;
+
+namespace Microsoft.VisualStudio.LanguageServices.Razor
+{
+    internal class DefaultFileChangeTracker : FileChangeTracker, IVsFileChangeEvents
+    {
+        private const uint FileChangeFlags = (uint)(_VSFILECHANGEFLAGS.VSFILECHG_Time | _VSFILECHANGEFLAGS.VSFILECHG_Size | _VSFILECHANGEFLAGS.VSFILECHG_Del | _VSFILECHANGEFLAGS.VSFILECHG_Add);
+
+        private readonly ForegroundDispatcher _foregroundDispatcher;
+        private readonly ErrorReporter _errorReporter;
+        private readonly IVsFileChangeEx _fileChangeService;
+        private uint _fileChangeCookie;
+
+        public override event EventHandler<FileChangeEventArgs> Changed;
+
+        public DefaultFileChangeTracker(
+            string filePath,
+            ForegroundDispatcher foregroundDispatcher,
+            ErrorReporter errorReporter,
+            IVsFileChangeEx fileChangeService)
+        {
+            if (string.IsNullOrEmpty(filePath))
+            {
+                throw new ArgumentException(Resources.ArgumentCannotBeNullOrEmpty, nameof(filePath));
+            }
+
+            if (foregroundDispatcher == null)
+            {
+                throw new ArgumentNullException(nameof(foregroundDispatcher));
+            }
+
+            if (errorReporter == null)
+            {
+                throw new ArgumentNullException(nameof(errorReporter));
+            }
+
+            if (fileChangeService == null)
+            {
+                throw new ArgumentNullException(nameof(fileChangeService));
+            }
+
+            FilePath = filePath;
+            _foregroundDispatcher = foregroundDispatcher;
+            _errorReporter = errorReporter;
+            _fileChangeService = fileChangeService;
+            _fileChangeCookie = VSConstants.VSCOOKIE_NIL;
+        }
+
+        public override string FilePath { get; }
+
+        public override void StartListening()
+        {
+            _foregroundDispatcher.AssertForegroundThread();
+
+            try
+            {
+                if (_fileChangeCookie == VSConstants.VSCOOKIE_NIL)
+                {
+                    var hr = _fileChangeService.AdviseFileChange(
+                        FilePath,
+                        FileChangeFlags,
+                        this,
+                        out _fileChangeCookie);
+
+                    Marshal.ThrowExceptionForHR(hr);
+                }
+            }
+            catch (Exception exception)
+            {
+                _errorReporter.ReportError(exception);
+            }
+        }
+
+        public override void StopListening()
+        {
+            _foregroundDispatcher.AssertForegroundThread();
+
+            try
+            {
+                if (_fileChangeCookie != VSConstants.VSCOOKIE_NIL)
+                {
+                    var hr = _fileChangeService.UnadviseFileChange(_fileChangeCookie);
+                    Marshal.ThrowExceptionForHR(hr);
+                    _fileChangeCookie = VSConstants.VSCOOKIE_NIL;
+                }
+            }
+            catch (Exception exception)
+            {
+                _errorReporter.ReportError(exception);
+            }
+        }
+
+        public int FilesChanged(uint fileCount, string[] filePaths, uint[] fileChangeFlags)
+        {
+            _foregroundDispatcher.AssertForegroundThread();
+
+            foreach (var fileChangeFlag in fileChangeFlags)
+            {
+                var fileChangeKind = FileChangeKind.Changed;
+                var changeFlag = (_VSFILECHANGEFLAGS)fileChangeFlag;
+                if ((changeFlag & _VSFILECHANGEFLAGS.VSFILECHG_Del) == _VSFILECHANGEFLAGS.VSFILECHG_Del)
+                {
+                    fileChangeKind = FileChangeKind.Removed;
+                }
+                else if ((changeFlag & _VSFILECHANGEFLAGS.VSFILECHG_Add) == _VSFILECHANGEFLAGS.VSFILECHG_Add)
+                {
+                    fileChangeKind = FileChangeKind.Added;
+                }
+
+                // Purposefully not passing through the file paths here because we know this change has to do with this trackers FilePath.
+                // We use that FilePath instead so any path normalization the file service did does not impact callers.
+                OnChanged(fileChangeKind);
+            }
+
+            return VSConstants.S_OK;
+        }
+
+        public int DirectoryChanged(string pszDirectory) => VSConstants.S_OK;
+
+        private void OnChanged(FileChangeKind changeKind)
+        {
+            _foregroundDispatcher.AssertForegroundThread();
+
+            if (Changed == null)
+            {
+                return;
+            }
+
+            var args = new FileChangeEventArgs(FilePath, changeKind);
+            Changed.Invoke(this, args);
+        }
+    }
+}

src/Microsoft.VisualStudio.LanguageServices.Razor/DefaultFileChangeTrackerFactory.cs

@@ -0,0 +1,53 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using Microsoft.CodeAnalysis.Razor;
+using Microsoft.VisualStudio.Editor.Razor;
+using Microsoft.VisualStudio.Shell.Interop;
+
+namespace Microsoft.VisualStudio.LanguageServices.Razor
+{
+    internal partial class DefaultFileChangeTrackerFactory : FileChangeTrackerFactory
+    {
+        private readonly ForegroundDispatcher _foregroundDispatcher;
+        private readonly ErrorReporter _errorReporter;
+        private readonly IVsFileChangeEx _fileChangeService;
+
+        public DefaultFileChangeTrackerFactory(
+            ForegroundDispatcher foregroundDispatcher,
+            ErrorReporter errorReporter, 
+            IVsFileChangeEx fileChangeService)
+        {
+            if (foregroundDispatcher == null)
+            {
+                throw new ArgumentNullException(nameof(foregroundDispatcher));
+            }
+
+            if (errorReporter == null)
+            {
+                throw new ArgumentNullException(nameof(errorReporter));
+            }
+
+            if (fileChangeService == null)
+            {
+                throw new ArgumentNullException(nameof(fileChangeService));
+            }
+
+            _foregroundDispatcher = foregroundDispatcher;
+            _errorReporter = errorReporter;
+            _fileChangeService = fileChangeService;
+        }
+
+        public override FileChangeTracker Create(string filePath)
+        {
+            if (string.IsNullOrEmpty(filePath))
+            {
+                throw new ArgumentException(Resources.ArgumentCannotBeNullOrEmpty, nameof(filePath));
+            }
+
+            var fileChangeTracker = new DefaultFileChangeTracker(filePath, _foregroundDispatcher, _errorReporter, _fileChangeService);
+            return fileChangeTracker;
+        }
+    }
+}

src/Microsoft.VisualStudio.LanguageServices.Razor/DefaultFileChangeTrackerFactoryFactory.cs

@@ -0,0 +1,44 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using System.Composition;
+using Microsoft.CodeAnalysis.Host;
+using Microsoft.CodeAnalysis.Host.Mef;
+using Microsoft.CodeAnalysis.Razor;
+using Microsoft.VisualStudio.Editor.Razor;
+using Microsoft.VisualStudio.Shell;
+using Microsoft.VisualStudio.Shell.Interop;
+
+namespace Microsoft.VisualStudio.LanguageServices.Razor
+{
+    [Shared]
+    [ExportLanguageServiceFactory(typeof(FileChangeTrackerFactory), RazorLanguage.Name, ServiceLayer.Default)]
+    internal class DefaultFileChangeTrackerFactoryFactory : ILanguageServiceFactory
+    {
+        private readonly IVsFileChangeEx _fileChangeService;
+
+        [ImportingConstructor]
+        public DefaultFileChangeTrackerFactoryFactory(SVsServiceProvider serviceProvider)
+        {
+            if (serviceProvider == null)
+            {
+                throw new ArgumentNullException(nameof(serviceProvider));
+            }
+
+            _fileChangeService = serviceProvider.GetService(typeof(SVsFileChangeEx)) as IVsFileChangeEx;
+        }
+
+        public ILanguageService CreateLanguageService(HostLanguageServices languageServices)
+        {
+            if (languageServices == null)
+            {
+                throw new ArgumentNullException(nameof(languageServices));
+            }
+
+            var foregroundDispatcher = languageServices.WorkspaceServices.GetRequiredService<ForegroundDispatcher>();
+            var errorReporter = languageServices.WorkspaceServices.GetRequiredService<ErrorReporter>();
+            return new DefaultFileChangeTrackerFactory(foregroundDispatcher, errorReporter, _fileChangeService);
+        }
+    }
+}

src/Microsoft.VisualStudio.LanguageServices.Razor/DefaultImportDocumentManager.cs

@@ -1,255 +0,0 @@
-// Copyright (c) .NET Foundation. All rights reserved.
-// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
-
-using System;
-using System.Collections.Generic;
-using System.ComponentModel.Composition;
-using System.Diagnostics;
-using System.IO;
-using System.Runtime.InteropServices;
-using Microsoft.AspNetCore.Razor.Language;
-using Microsoft.CodeAnalysis.Razor;
-using Microsoft.VisualStudio.Editor.Razor;
-using Microsoft.VisualStudio.Shell;
-using Microsoft.VisualStudio.Shell.Interop;
-
-namespace Microsoft.VisualStudio.LanguageServices.Razor
-{
-    [System.Composition.Shared]
-    [Export(typeof(ImportDocumentManager))]
-    internal class DefaultImportDocumentManager : ImportDocumentManager
-    {
-        private const uint FileChangeFlags = (uint)(_VSFILECHANGEFLAGS.VSFILECHG_Time | _VSFILECHANGEFLAGS.VSFILECHG_Size | _VSFILECHANGEFLAGS.VSFILECHG_Del | _VSFILECHANGEFLAGS.VSFILECHG_Add);
-
-        private readonly IVsFileChangeEx _fileChangeService;
-        private readonly ForegroundDispatcher _foregroundDispatcher;
-        private readonly ErrorReporter _errorReporter;
-        private readonly RazorTemplateEngineFactoryService _templateEngineFactoryService;
-        private readonly Dictionary<string, ImportTracker> _importTrackerCache;
-
-        public override event EventHandler<ImportChangedEventArgs> Changed;
-
-        [ImportingConstructor]
-        public DefaultImportDocumentManager(
-            [Import(typeof(SVsServiceProvider))] IServiceProvider serviceProvider,
-            VisualStudioWorkspaceAccessor workspaceAccessor)
-        {
-            if (serviceProvider == null)
-            {
-                throw new ArgumentNullException(nameof(serviceProvider));
-            }
-
-            if (workspaceAccessor == null)
-            {
-                throw new ArgumentNullException(nameof(workspaceAccessor));
-            }
-
-            _fileChangeService = serviceProvider.GetService(typeof(SVsFileChangeEx)) as IVsFileChangeEx;
-
-            var workspace = workspaceAccessor.Workspace;
-            _foregroundDispatcher = workspace.Services.GetRequiredService<ForegroundDispatcher>();
-            _errorReporter = workspace.Services.GetRequiredService<ErrorReporter>();
-
-            var razorLanguageServices = workspace.Services.GetLanguageServices(RazorLanguage.Name);
-            _templateEngineFactoryService = razorLanguageServices.GetRequiredService<RazorTemplateEngineFactoryService>();
-
-            _importTrackerCache = new Dictionary<string, ImportTracker>(StringComparer.OrdinalIgnoreCase);
-        }
-
-        // This is only used for testing.
-        internal DefaultImportDocumentManager(
-            IVsFileChangeEx fileChangeService,
-            RazorTemplateEngineFactoryService templateEngineFactoryService,
-            ForegroundDispatcher foregroundDispatcher,
-            ErrorReporter errorReporter)
-        {
-            _fileChangeService = fileChangeService;
-            _templateEngineFactoryService = templateEngineFactoryService;
-            _foregroundDispatcher = foregroundDispatcher;
-            _errorReporter = errorReporter;
-
-            _importTrackerCache = new Dictionary<string, ImportTracker>(StringComparer.OrdinalIgnoreCase);
-        }
-
-        public override void OnSubscribed(VisualStudioDocumentTracker tracker)
-        {
-            if (tracker == null)
-            {
-                throw new ArgumentNullException(nameof(tracker));
-            }
-
-            _foregroundDispatcher.AssertForegroundThread();
-
-            var imports = GetImportItems(tracker);
-            foreach (var import in imports)
-            {
-                var importFilePath = import.PhysicalPath;
-                Debug.Assert(importFilePath != null);
-
-                if (!_importTrackerCache.TryGetValue(importFilePath, out var importTracker))
-                {
-                    // First time seeing this import. Start tracking it.
-                    importTracker = new ImportTracker(importFilePath);
-                    _importTrackerCache[importFilePath] = importTracker;
-
-                    StartListeningForChanges(importTracker);
-                }
-
-                importTracker.AssociatedDocuments.Add(tracker.FilePath);
-            }
-        }
-
-        public override void OnUnsubscribed(VisualStudioDocumentTracker tracker)
-        {
-            if (tracker == null)
-            {
-                throw new ArgumentNullException(nameof(tracker));
-            }
-
-            _foregroundDispatcher.AssertForegroundThread();
-
-            var imports = GetImportItems(tracker);
-            foreach (var import in imports)
-            {
-                var importFilePath = import.PhysicalPath;
-                Debug.Assert(importFilePath != null);
-
-                if (_importTrackerCache.TryGetValue(importFilePath, out var importTracker))
-                {
-                    importTracker.AssociatedDocuments.Remove(tracker.FilePath);
-
-                    if (importTracker.AssociatedDocuments.Count == 0)
-                    {
-                        // There are no open documents that care about this import. We no longer need to track it.
-                        StopListeningForChanges(importTracker);
-                        _importTrackerCache.Remove(importFilePath);
-                    }
-                }
-            }
-        }
-
-        private IEnumerable<RazorProjectItem> GetImportItems(VisualStudioDocumentTracker tracker)
-        {
-            var projectDirectory = Path.GetDirectoryName(tracker.ProjectPath);
-            var templateEngine = _templateEngineFactoryService.Create(projectDirectory, _ => { });
-            var imports = templateEngine.GetImportItems(tracker.FilePath);
-
-            return imports;
-        }
-
-        private void FireImportChanged(string importPath, ImportChangeKind kind)
-        {
-            _foregroundDispatcher.AssertForegroundThread();
-
-            var handler = Changed;
-            if (handler != null && _importTrackerCache.TryGetValue(importPath, out var importTracker))
-            {
-                var args = new ImportChangedEventArgs(importPath, kind, importTracker.AssociatedDocuments);
-                handler(this, args);
-            }
-        }
-
-        // internal for testing.
-        internal void OnFilesChanged(uint fileCount, string[] filePaths, uint[] fileChangeFlags)
-        {
-            for (var i = 0; i < fileCount; i++)
-            {
-                var kind = ImportChangeKind.Changed;
-                var flag = (_VSFILECHANGEFLAGS)fileChangeFlags[i];
-
-                if ((flag & _VSFILECHANGEFLAGS.VSFILECHG_Del) == _VSFILECHANGEFLAGS.VSFILECHG_Del)
-                {
-                    kind = ImportChangeKind.Removed;
-                }
-                else if ((flag & _VSFILECHANGEFLAGS.VSFILECHG_Add) == _VSFILECHANGEFLAGS.VSFILECHG_Add)
-                {
-                    kind = ImportChangeKind.Added;
-                }
-
-                FireImportChanged(filePaths[i], kind);
-            }
-        }
-
-        private void StartListeningForChanges(ImportTracker importTracker)
-        {
-            try
-            {
-                if (importTracker.FileChangeCookie == VSConstants.VSCOOKIE_NIL)
-                {
-                    var hr = _fileChangeService.AdviseFileChange(
-                            importTracker.FilePath,
-                            FileChangeFlags,
-                            new ImportDocumentEventSink(this, _foregroundDispatcher),
-                            out var cookie);
-
-                    Marshal.ThrowExceptionForHR(hr);
-
-                    importTracker.FileChangeCookie = cookie;
-                }
-            }
-            catch (Exception exception)
-            {
-                _errorReporter.ReportError(exception);
-            }
-        }
-
-        private void StopListeningForChanges(ImportTracker importTracker)
-        {
-            try
-            {
-                if (importTracker.FileChangeCookie != VSConstants.VSCOOKIE_NIL)
-                {
-                    var hr = _fileChangeService.UnadviseFileChange(importTracker.FileChangeCookie);
-                    Marshal.ThrowExceptionForHR(hr);
-                    importTracker.FileChangeCookie = VSConstants.VSCOOKIE_NIL;
-                }
-            }
-            catch (Exception exception)
-            {
-                _errorReporter.ReportError(exception);
-            }
-        }
-
-        private class ImportTracker
-        {
-            public ImportTracker(string filePath)
-            {
-                FilePath = filePath;
-                AssociatedDocuments = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
-                FileChangeCookie = VSConstants.VSCOOKIE_NIL;
-            }
-
-            public string FilePath { get; }
-
-            public HashSet<string> AssociatedDocuments { get; }
-
-            public uint FileChangeCookie { get; set; }
-        }
-
-        private class ImportDocumentEventSink : IVsFileChangeEvents
-        {
-            private readonly DefaultImportDocumentManager _importDocumentManager;
-            private readonly ForegroundDispatcher _foregroundDispatcher;
-
-            public ImportDocumentEventSink(DefaultImportDocumentManager importDocumentManager, ForegroundDispatcher foregroundDispatcher)
-            {
-                _importDocumentManager = importDocumentManager;
-                _foregroundDispatcher = foregroundDispatcher;
-            }
-
-            public int FilesChanged(uint cChanges, string[] rgpszFile, uint[] rggrfChange)
-            {
-                _foregroundDispatcher.AssertForegroundThread();
-
-                _importDocumentManager.OnFilesChanged(cChanges, rgpszFile, rggrfChange);
-
-                return VSConstants.S_OK;
-            }
-
-            public int DirectoryChanged(string pszDirectory)
-            {
-                return VSConstants.S_OK;
-            }
-        }
-    }
-}

test/Microsoft.VisualStudio.Editor.Razor.Test/DefaultImportDocumentManagerIntegrationTest.cs

@@ -0,0 +1,70 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using Microsoft.CodeAnalysis.Razor;
+using Microsoft.CodeAnalysis.Razor.ProjectSystem;
+using Moq;
+using Xunit;
+
+namespace Microsoft.VisualStudio.Editor.Razor
+{
+    public class DefaultImportDocumentManagerIntegrationTest : ForegroundDispatcherTestBase
+    {
+        [ForegroundFact]
+        public void Changed_TrackerChanged_ResultsInChangedHavingCorrectArgs()
+        {
+            // Arrange
+            var filePath = "C:\\path\\to\\project\\Views\\Home\\file.cshtml";
+            var anotherFilePath = "C:\\path\\to\\project\\anotherFile.cshtml";
+            var projectPath = "C:\\path\\to\\project\\project.csproj";
+            var testImportsPath = "C:\\path\\to\\project\\_ViewImports.cshtml";
+            var tracker = Mock.Of<VisualStudioDocumentTracker>(t => t.FilePath == filePath && t.ProjectPath == projectPath);
+            var anotherTracker = Mock.Of<VisualStudioDocumentTracker>(t => t.FilePath == anotherFilePath && t.ProjectPath == projectPath);
+            var templateEngineFactoryService = GetTemplateEngineFactoryService();
+            var fileChangeTracker = new Mock<FileChangeTracker>();
+            fileChangeTracker.Setup(f => f.FilePath).Returns(testImportsPath);
+            var fileChangeTrackerFactory = new Mock<FileChangeTrackerFactory>();
+            fileChangeTrackerFactory
+                .Setup(f => f.Create(testImportsPath))
+                .Returns(fileChangeTracker.Object);
+            fileChangeTrackerFactory
+                .Setup(f => f.Create("C:\\path\\to\\project\\Views\\_ViewImports.cshtml"))
+                .Returns(Mock.Of<FileChangeTracker>());
+            fileChangeTrackerFactory
+                .Setup(f => f.Create("C:\\path\\to\\project\\Views\\Home\\_ViewImports.cshtml"))
+                .Returns(Mock.Of<FileChangeTracker>());
+
+            var called = false;
+            var manager = new DefaultImportDocumentManager(Dispatcher, new DefaultErrorReporter(), fileChangeTrackerFactory.Object, templateEngineFactoryService);
+            manager.OnSubscribed(tracker);
+            manager.OnSubscribed(anotherTracker);
+            manager.Changed += (sender, args) =>
+            {
+                called = true;
+                Assert.Same(sender, manager);
+                Assert.Equal(testImportsPath, args.FilePath);
+                Assert.Equal(FileChangeKind.Changed, args.Kind);
+                Assert.Collection(
+                    args.AssociatedDocuments,
+                    f => Assert.Equal(filePath, f),
+                    f => Assert.Equal(anotherFilePath, f));
+            };
+
+            // Act
+            fileChangeTracker.Raise(t => t.Changed += null, new FileChangeEventArgs(testImportsPath, FileChangeKind.Changed));
+
+            // Assert
+            Assert.True(called);
+        }
+
+        private RazorTemplateEngineFactoryService GetTemplateEngineFactoryService()
+        {
+            var projectManager = new Mock<ProjectSnapshotManager>();
+            projectManager.Setup(p => p.Projects).Returns(Array.Empty<ProjectSnapshot>());
+
+            var service = new DefaultTemplateEngineFactoryService(projectManager.Object);
+            return service;
+        }
+    }
+}

test/Microsoft.VisualStudio.Editor.Razor.Test/DefaultImportDocumentManagerTest.cs

@@ -0,0 +1,149 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using Microsoft.CodeAnalysis.Razor;
+using Microsoft.CodeAnalysis.Razor.ProjectSystem;
+using Moq;
+using Xunit;
+
+namespace Microsoft.VisualStudio.Editor.Razor
+{
+    public class DefaultImportDocumentManagerTest : ForegroundDispatcherTestBase
+    {
+        [ForegroundFact]
+        public void OnSubscribed_StartsFileChangeTrackers()
+        {
+            // Arrange
+            var filePath = "C:\\path\\to\\project\\Views\\Home\\file.cshtml";
+            var projectPath = "C:\\path\\to\\project\\project.csproj";
+            var tracker = Mock.Of<VisualStudioDocumentTracker>(t => t.FilePath == filePath && t.ProjectPath == projectPath);
+            var templateEngineFactoryService = GetTemplateEngineFactoryService();
+            var fileChangeTracker1 = new Mock<FileChangeTracker>();
+            fileChangeTracker1.Setup(f => f.StartListening()).Verifiable();
+            var fileChangeTrackerFactory = new Mock<FileChangeTrackerFactory>();
+            fileChangeTrackerFactory
+                .Setup(f => f.Create("C:\\path\\to\\project\\Views\\Home\\_ViewImports.cshtml"))
+                .Returns(fileChangeTracker1.Object)
+                .Verifiable();
+            var fileChangeTracker2 = new Mock<FileChangeTracker>();
+            fileChangeTracker2.Setup(f => f.StartListening()).Verifiable();
+            fileChangeTrackerFactory
+                .Setup(f => f.Create("C:\\path\\to\\project\\Views\\_ViewImports.cshtml"))
+                .Returns(fileChangeTracker2.Object)
+                .Verifiable();
+            var fileChangeTracker3 = new Mock<FileChangeTracker>();
+            fileChangeTracker3.Setup(f => f.StartListening()).Verifiable();
+            fileChangeTrackerFactory
+                .Setup(f => f.Create("C:\\path\\to\\project\\_ViewImports.cshtml"))
+                .Returns(fileChangeTracker3.Object)
+                .Verifiable();
+
+            var manager = new DefaultImportDocumentManager(Dispatcher, new DefaultErrorReporter(), fileChangeTrackerFactory.Object, templateEngineFactoryService);
+
+            // Act
+            manager.OnSubscribed(tracker);
+
+            // Assert
+            fileChangeTrackerFactory.Verify();
+            fileChangeTracker1.Verify();
+            fileChangeTracker2.Verify();
+            fileChangeTracker3.Verify();
+        }
+
+        [ForegroundFact]
+        public void OnSubscribed_AlreadySubscribed_DoesNothing()
+        {
+            // Arrange
+            var filePath = "C:\\path\\to\\project\\file.cshtml";
+            var projectPath = "C:\\path\\to\\project\\project.csproj";
+            var tracker = Mock.Of<VisualStudioDocumentTracker>(t => t.FilePath == filePath && t.ProjectPath == projectPath);
+            var templateEngineFactoryService = GetTemplateEngineFactoryService();
+
+            var callCount = 0;
+            var fileChangeTrackerFactory = new Mock<FileChangeTrackerFactory>();
+            fileChangeTrackerFactory
+                .Setup(f => f.Create(It.IsAny<string>()))
+                .Returns(Mock.Of<FileChangeTracker>())
+                .Callback(() => callCount++);
+
+            var manager = new DefaultImportDocumentManager(Dispatcher, new DefaultErrorReporter(), fileChangeTrackerFactory.Object, templateEngineFactoryService);
+            manager.OnSubscribed(tracker); // Start tracking the import.
+
+            var anotherFilePath = "C:\\path\\to\\project\\anotherFile.cshtml";
+            var anotherTracker = Mock.Of<VisualStudioDocumentTracker>(t => t.FilePath == anotherFilePath && t.ProjectPath == projectPath);
+
+            // Act
+            manager.OnSubscribed(anotherTracker);
+
+            // Assert
+            Assert.Equal(1, callCount);
+        }
+
+        [ForegroundFact]
+        public void OnUnsubscribed_StopsFileChangeTracker()
+        {
+            // Arrange
+            var filePath = "C:\\path\\to\\project\\file.cshtml";
+            var projectPath = "C:\\path\\to\\project\\project.csproj";
+            var tracker = Mock.Of<VisualStudioDocumentTracker>(t => t.FilePath == filePath && t.ProjectPath == projectPath);
+            var templateEngineFactoryService = GetTemplateEngineFactoryService();
+
+            var fileChangeTracker = new Mock<FileChangeTracker>();
+            fileChangeTracker.Setup(f => f.StopListening()).Verifiable();
+            var fileChangeTrackerFactory = new Mock<FileChangeTrackerFactory>(MockBehavior.Strict);
+            fileChangeTrackerFactory
+                .Setup(f => f.Create("C:\\path\\to\\project\\_ViewImports.cshtml"))
+                .Returns(fileChangeTracker.Object)
+                .Verifiable();
+
+            var manager = new DefaultImportDocumentManager(Dispatcher, new DefaultErrorReporter(), fileChangeTrackerFactory.Object, templateEngineFactoryService);
+            manager.OnSubscribed(tracker); // Start tracking the import.
+
+            // Act
+            manager.OnUnsubscribed(tracker);
+
+            // Assert
+            fileChangeTrackerFactory.Verify();
+            fileChangeTracker.Verify();
+        }
+
+        [ForegroundFact]
+        public void OnUnsubscribed_AnotherDocumentTrackingImport_DoesNotStopFileChangeTracker()
+        {
+            // Arrange
+            var filePath = "C:\\path\\to\\project\\file.cshtml";
+            var projectPath = "C:\\path\\to\\project\\project.csproj";
+            var tracker = Mock.Of<VisualStudioDocumentTracker>(t => t.FilePath == filePath && t.ProjectPath == projectPath);
+            var templateEngineFactoryService = GetTemplateEngineFactoryService();
+
+            var fileChangeTracker = new Mock<FileChangeTracker>();
+            fileChangeTracker
+                .Setup(f => f.StopListening())
+                .Throws(new InvalidOperationException());
+            var fileChangeTrackerFactory = new Mock<FileChangeTrackerFactory>();
+            fileChangeTrackerFactory
+                .Setup(f => f.Create(It.IsAny<string>()))
+                .Returns(fileChangeTracker.Object);
+
+            var manager = new DefaultImportDocumentManager(Dispatcher, new DefaultErrorReporter(), fileChangeTrackerFactory.Object, templateEngineFactoryService);
+            manager.OnSubscribed(tracker); // Starts tracking import for the first document.
+
+            var anotherFilePath = "C:\\path\\to\\project\\anotherFile.cshtml";
+            var anotherTracker = Mock.Of<VisualStudioDocumentTracker>(t => t.FilePath == anotherFilePath && t.ProjectPath == projectPath);
+            manager.OnSubscribed(anotherTracker); // Starts tracking import for the second document.
+
+            // Act & Assert (Does not throw)
+            manager.OnUnsubscribed(tracker);
+        }
+
+        private RazorTemplateEngineFactoryService GetTemplateEngineFactoryService()
+        {
+            var projectManager = new Mock<ProjectSnapshotManager>();
+            projectManager.Setup(p => p.Projects).Returns(Array.Empty<ProjectSnapshot>());
+
+            var service = new DefaultTemplateEngineFactoryService(projectManager.Object);
+            return service;
+        }
+    }
+}

test/Microsoft.VisualStudio.Editor.Razor.Test/DefaultVisualStudioDocumentTrackerTest.cs

@@ -137,7 +137,7 @@ namespace Microsoft.VisualStudio.Editor.Razor
                 called = true;
             };
 
-            var importChangedArgs = new ImportChangedEventArgs("path/to/import", ImportChangeKind.Changed, new[] { FilePath });
+            var importChangedArgs = new ImportChangedEventArgs("path/to/import", FileChangeKind.Changed, new[] { FilePath });
 
             // Act
             documentTracker.Import_Changed(null, importChangedArgs);
@@ -157,7 +157,7 @@ namespace Microsoft.VisualStudio.Editor.Razor
                 throw new InvalidOperationException();
             };
 
-            var importChangedArgs = new ImportChangedEventArgs("path/to/import", ImportChangeKind.Changed, new[] { "path/to/differentfile" });
+            var importChangedArgs = new ImportChangedEventArgs("path/to/import", FileChangeKind.Changed, new[] { "path/to/differentfile" });
 
             // Act & Assert (Does not throw)
             documentTracker.Import_Changed(null, importChangedArgs);

test/Microsoft.VisualStudio.LanguageServices.Razor.Test/DefaultFileChangeTrackerTest.cs

@@ -0,0 +1,128 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using Microsoft.CodeAnalysis.Razor;
+using Microsoft.VisualStudio.Editor.Razor;
+using Microsoft.VisualStudio.Shell.Interop;
+using Moq;
+using Xunit;
+
+namespace Microsoft.VisualStudio.LanguageServices.Razor
+{
+    public class DefaultFileChangeTrackerTest : ForegroundDispatcherTestBase
+    {
+        private ErrorReporter ErrorReporter { get; } = new DefaultErrorReporter();
+
+        [ForegroundFact]
+        public void StartListening_AdvisesForFileChange()
+        {
+            // Arrange
+            uint cookie;
+            var fileChangeService = new Mock<IVsFileChangeEx>();
+            fileChangeService
+                .Setup(f => f.AdviseFileChange(It.IsAny<string>(), It.IsAny<uint>(), It.IsAny<IVsFileChangeEvents>(), out cookie))
+                .Returns(VSConstants.S_OK)
+                .Verifiable();
+            var tracker = new DefaultFileChangeTracker("C:/_ViewImports.cshtml", Dispatcher, ErrorReporter, fileChangeService.Object);
+
+            // Act
+            tracker.StartListening();
+
+            // Assert
+            fileChangeService.Verify();
+        }
+
+        [ForegroundFact]
+        public void StartListening_AlreadyListening_DoesNothing()
+        {
+            // Arrange
+            uint cookie = 100;
+            var callCount = 0;
+            var fileChangeService = new Mock<IVsFileChangeEx>();
+            fileChangeService
+                .Setup(f => f.AdviseFileChange(It.IsAny<string>(), It.IsAny<uint>(), It.IsAny<IVsFileChangeEvents>(), out cookie))
+                .Returns(VSConstants.S_OK)
+                .Callback(() => callCount++);
+            var tracker = new DefaultFileChangeTracker("C:/_ViewImports.cshtml", Dispatcher, ErrorReporter, fileChangeService.Object);
+            tracker.StartListening();
+
+            // Act
+            tracker.StartListening();
+
+            // Assert
+            Assert.Equal(1, callCount);
+        }
+
+        [ForegroundFact]
+        public void StopListening_UnadvisesForFileChange()
+        {
+            // Arrange
+            uint cookie = 100;
+            var fileChangeService = new Mock<IVsFileChangeEx>(MockBehavior.Strict);
+            fileChangeService
+                .Setup(f => f.AdviseFileChange(It.IsAny<string>(), It.IsAny<uint>(), It.IsAny<IVsFileChangeEvents>(), out cookie))
+                .Returns(VSConstants.S_OK)
+                .Verifiable();
+            fileChangeService
+                .Setup(f => f.UnadviseFileChange(cookie))
+                .Returns(VSConstants.S_OK)
+                .Verifiable();
+            var tracker = new DefaultFileChangeTracker("C:/_ViewImports.cshtml", Dispatcher, ErrorReporter, fileChangeService.Object);
+            tracker.StartListening(); // Start listening for changes.
+
+            // Act
+            tracker.StopListening();
+
+            // Assert
+            fileChangeService.Verify();
+        }
+
+        [ForegroundFact]
+        public void StartListening_NotListening_DoesNothing()
+        {
+            // Arrange
+            uint cookie = VSConstants.VSCOOKIE_NIL;
+            var fileChangeService = new Mock<IVsFileChangeEx>(MockBehavior.Strict);
+            fileChangeService
+                .Setup(f => f.UnadviseFileChange(cookie))
+                .Throws(new InvalidOperationException());
+            var tracker = new DefaultFileChangeTracker("C:/_ViewImports.cshtml", Dispatcher, ErrorReporter, fileChangeService.Object);
+
+            // Act & Assert
+            tracker.StopListening();
+        }
+
+        [ForegroundTheory]
+        [InlineData((uint)_VSFILECHANGEFLAGS.VSFILECHG_Size, (int)FileChangeKind.Changed)]
+        [InlineData((uint)_VSFILECHANGEFLAGS.VSFILECHG_Time, (int)FileChangeKind.Changed)]
+        [InlineData((uint)_VSFILECHANGEFLAGS.VSFILECHG_Add, (int)FileChangeKind.Added)]
+        [InlineData((uint)_VSFILECHANGEFLAGS.VSFILECHG_Del, (int)FileChangeKind.Removed)]
+        public void FilesChanged_WithSpecificFlags_InvokesChangedHandler_WithExpectedArguments(uint fileChangeFlag, int expectedKind)
+        {
+            // Arrange
+            var filePath = "C:\\path\\to\\project\\_ViewImports.cshtml";
+            uint cookie;
+            var fileChangeService = new Mock<IVsFileChangeEx>();
+            fileChangeService
+                .Setup(f => f.AdviseFileChange(It.IsAny<string>(), It.IsAny<uint>(), It.IsAny<IVsFileChangeEvents>(), out cookie))
+                .Returns(VSConstants.S_OK);
+            var tracker = new DefaultFileChangeTracker(filePath, Dispatcher, ErrorReporter, fileChangeService.Object);
+            
+            var called = false;
+            tracker.Changed += (sender, args) =>
+            {
+                called = true;
+                Assert.Same(sender, tracker);
+                Assert.Equal(filePath, args.FilePath);
+                Assert.Equal((FileChangeKind)expectedKind, args.Kind);
+            };
+
+            // Act
+            tracker.FilesChanged(fileCount: 1, filePaths: new[] { filePath }, fileChangeFlags: new[] { fileChangeFlag });
+
+            // Assert
+            Assert.True(called);
+        }
+    }
+}

test/Microsoft.VisualStudio.LanguageServices.Razor.Test/DefaultImportDocumentManagerTest.cs

@@ -1,193 +0,0 @@
-// Copyright (c) .NET Foundation. All rights reserved.
-// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
-
-using System;
-using Microsoft.CodeAnalysis.Razor;
-using Microsoft.CodeAnalysis.Razor.ProjectSystem;
-using Microsoft.VisualStudio.Editor.Razor;
-using Microsoft.VisualStudio.Shell.Interop;
-using Moq;
-using Xunit;
-
-namespace Microsoft.VisualStudio.LanguageServices.Razor
-{
-    public class DefaultImportDocumentManagerTest : ForegroundDispatcherTestBase
-    {
-        [ForegroundFact]
-        public void OnSubscribed_StartTrackingImport()
-        {
-            // Arrange
-            var filePath = "C:\\path\\to\\project\\Views\\Home\\file.cshtml";
-            var projectPath = "C:\\path\\to\\project\\project.csproj";
-            var tracker = Mock.Of<VisualStudioDocumentTracker>(t => t.FilePath == filePath && t.ProjectPath == projectPath);
-            var templateEngineFactoryService = GetTemplateEngineFactoryService();
-
-            uint cookie;
-            var fileChangeService = new Mock<IVsFileChangeEx>(MockBehavior.Strict);
-            fileChangeService
-                .Setup(f => f.AdviseFileChange("C:\\path\\to\\project\\Views\\Home\\_ViewImports.cshtml", It.IsAny<uint>(), It.IsAny<IVsFileChangeEvents>(), out cookie))
-                .Returns(VSConstants.S_OK)
-                .Verifiable();
-            fileChangeService
-                .Setup(f => f.AdviseFileChange("C:\\path\\to\\project\\Views\\_ViewImports.cshtml", It.IsAny<uint>(), It.IsAny<IVsFileChangeEvents>(), out cookie))
-                .Returns(VSConstants.S_OK)
-                .Verifiable();
-            fileChangeService
-                .Setup(f => f.AdviseFileChange("C:\\path\\to\\project\\_ViewImports.cshtml", It.IsAny<uint>(), It.IsAny<IVsFileChangeEvents>(), out cookie))
-                .Returns(VSConstants.S_OK)
-                .Verifiable();
-
-            var manager = new DefaultImportDocumentManager(fileChangeService.Object, templateEngineFactoryService, Dispatcher, new DefaultErrorReporter());
-
-            // Act
-            manager.OnSubscribed(tracker);
-
-            // Assert
-            fileChangeService.Verify();
-        }
-
-        [ForegroundFact]
-        public void OnSubscribed_AlreadyTrackingImport_DoesNothing()
-        {
-            // Arrange
-            var filePath = "C:\\path\\to\\project\\file.cshtml";
-            var projectPath = "C:\\path\\to\\project\\project.csproj";
-            var tracker = Mock.Of<VisualStudioDocumentTracker>(t => t.FilePath == filePath && t.ProjectPath == projectPath);
-            var templateEngineFactoryService = GetTemplateEngineFactoryService();
-
-            uint cookie;
-            var callCount = 0;
-            var fileChangeService = new Mock<IVsFileChangeEx>();
-            fileChangeService
-                .Setup(f => f.AdviseFileChange(It.IsAny<string>(), It.IsAny<uint>(), It.IsAny<IVsFileChangeEvents>(), out cookie))
-                .Returns(VSConstants.S_OK)
-                .Callback(() => callCount++);
-
-            var manager = new DefaultImportDocumentManager(fileChangeService.Object, templateEngineFactoryService, Dispatcher, new DefaultErrorReporter());
-            manager.OnSubscribed(tracker); // Start tracking the import.
-
-            var anotherFilePath = "C:\\path\\to\\project\\anotherFile.cshtml";
-            var anotherTracker = Mock.Of<VisualStudioDocumentTracker>(t => t.FilePath == anotherFilePath && t.ProjectPath == projectPath);
-
-            // Act
-            manager.OnSubscribed(anotherTracker);
-
-            // Assert
-            Assert.Equal(1, callCount);
-        }
-
-        [ForegroundFact]
-        public void OnUnsubscribed_StopsTrackingImport()
-        {
-            // Arrange
-            var filePath = "C:\\path\\to\\project\\file.cshtml";
-            var projectPath = "C:\\path\\to\\project\\project.csproj";
-            var tracker = Mock.Of<VisualStudioDocumentTracker>(t => t.FilePath == filePath && t.ProjectPath == projectPath);
-            var templateEngineFactoryService = GetTemplateEngineFactoryService();
-
-            uint cookie = 100;
-            var fileChangeService = new Mock<IVsFileChangeEx>(MockBehavior.Strict);
-            fileChangeService
-                .Setup(f => f.AdviseFileChange("C:\\path\\to\\project\\_ViewImports.cshtml", It.IsAny<uint>(), It.IsAny<IVsFileChangeEvents>(), out cookie))
-                .Returns(VSConstants.S_OK)
-                .Verifiable();
-            fileChangeService
-                .Setup(f => f.UnadviseFileChange(cookie))
-                .Returns(VSConstants.S_OK)
-                .Verifiable();
-
-            var manager = new DefaultImportDocumentManager(fileChangeService.Object, templateEngineFactoryService, Dispatcher, new DefaultErrorReporter());
-            manager.OnSubscribed(tracker); // Start tracking the import.
-
-            // Act
-            manager.OnUnsubscribed(tracker);
-
-            // Assert
-            fileChangeService.Verify();
-        }
-
-        [ForegroundFact]
-        public void OnUnsubscribed_AnotherDocumentTrackingImport_DoesNotStopTrackingImport()
-        {
-            // Arrange
-            var filePath = "C:\\path\\to\\project\\file.cshtml";
-            var projectPath = "C:\\path\\to\\project\\project.csproj";
-            var tracker = Mock.Of<VisualStudioDocumentTracker>(t => t.FilePath == filePath && t.ProjectPath == projectPath);
-            var templateEngineFactoryService = GetTemplateEngineFactoryService();
-
-            uint cookie;
-            var fileChangeService = new Mock<IVsFileChangeEx>();
-            fileChangeService
-                .Setup(f => f.AdviseFileChange(It.IsAny<string>(), It.IsAny<uint>(), It.IsAny<IVsFileChangeEvents>(), out cookie))
-                .Returns(VSConstants.S_OK);
-            fileChangeService
-                .Setup(f => f.UnadviseFileChange(It.IsAny<uint>()))
-                .Returns(VSConstants.S_OK)
-                .Callback(() => throw new InvalidOperationException());
-
-            var manager = new DefaultImportDocumentManager(fileChangeService.Object, templateEngineFactoryService, Dispatcher, new DefaultErrorReporter());
-            manager.OnSubscribed(tracker); // Starts tracking import for the first document.
-
-            var anotherFilePath = "C:\\path\\to\\project\\anotherFile.cshtml";
-            var anotherTracker = Mock.Of<VisualStudioDocumentTracker>(t => t.FilePath == anotherFilePath && t.ProjectPath == projectPath);
-            manager.OnSubscribed(anotherTracker); // Starts tracking import for the second document.
-
-            // Act & Assert (Does not throw)
-            manager.OnUnsubscribed(tracker);
-        }
-
-        [ForegroundTheory]
-        [InlineData((uint)_VSFILECHANGEFLAGS.VSFILECHG_Size, (int)ImportChangeKind.Changed)]
-        [InlineData((uint)_VSFILECHANGEFLAGS.VSFILECHG_Time, (int)ImportChangeKind.Changed)]
-        [InlineData((uint)_VSFILECHANGEFLAGS.VSFILECHG_Add, (int)ImportChangeKind.Added)]
-        [InlineData((uint)_VSFILECHANGEFLAGS.VSFILECHG_Del, (int)ImportChangeKind.Removed)]
-        public void OnFilesChanged_WithSpecificFlags_InvokesChangedHandler_WithExpectedArguments(uint fileChangeFlag, int expectedKind)
-        {
-            // Arrange
-            var filePath = "C:\\path\\to\\project\\file.cshtml";
-            var projectPath = "C:\\path\\to\\project\\project.csproj";
-            var tracker = Mock.Of<VisualStudioDocumentTracker>(t => t.FilePath == filePath && t.ProjectPath == projectPath);
-            var templateEngineFactoryService = GetTemplateEngineFactoryService();
-
-            var anotherFilePath = "C:\\path\\to\\project\\anotherFile.cshtml";
-            var anotherTracker = Mock.Of<VisualStudioDocumentTracker>(t => t.FilePath == anotherFilePath && t.ProjectPath == projectPath);
-
-            uint cookie;
-            var fileChangeService = new Mock<IVsFileChangeEx>();
-            fileChangeService
-                .Setup(f => f.AdviseFileChange(It.IsAny<string>(), It.IsAny<uint>(), It.IsAny<IVsFileChangeEvents>(), out cookie))
-                .Returns(VSConstants.S_OK);
-            var manager = new DefaultImportDocumentManager(fileChangeService.Object, templateEngineFactoryService, Dispatcher, new DefaultErrorReporter());
-            manager.OnSubscribed(tracker);
-            manager.OnSubscribed(anotherTracker);
-
-            var called = false;
-            manager.Changed += (sender, args) =>
-            {
-                called = true;
-                Assert.Same(sender, manager);
-                Assert.Equal("C:\\path\\to\\project\\_ViewImports.cshtml", args.FilePath);
-                Assert.Equal((ImportChangeKind)expectedKind, args.Kind);
-                Assert.Collection(
-                    args.AssociatedDocuments,
-                    f => Assert.Equal(filePath, f),
-                    f => Assert.Equal(anotherFilePath, f));
-            };
-
-            // Act
-            manager.OnFilesChanged(fileCount: 1, filePaths: new[] { "C:\\path\\to\\project\\_ViewImports.cshtml" }, fileChangeFlags: new[] { fileChangeFlag });
-
-            // Assert
-            Assert.True(called);
-        }
-
-        private RazorTemplateEngineFactoryService GetTemplateEngineFactoryService()
-        {
-            var projectManager = new Mock<ProjectSnapshotManager>();
-            projectManager.Setup(p => p.Projects).Returns(Array.Empty<ProjectSnapshot>());
-
-            var service = new DefaultTemplateEngineFactoryService(projectManager.Object);
-            return service;
-        }
-    }
-}