fix: null-handling in Wrap-Method in factories for IDriveInfo or IFileSystemWatcher (#977)

Building on #976 also fix null-handling for DriveInfo and FileSystemWatcher factories:
When providing null as parameter to the implementations of IDriveInfoFactory or IFileSystemWatcherFactory return null instead of throwing an exception.

This extends the issue reported in #975 to other factories used in System.IO.Abstractions.

Author: vbreuss

src/TestableIO.System.IO.Abstractions.TestingHelpers/MockDriveInfoFactory.cs

@@ -56,6 +56,11 @@ public IDriveInfo New(string driveName)
         /// <inheritdoc />
         public IDriveInfo Wrap(DriveInfo driveInfo)
         {
+            if (driveInfo == null)
+            {
+                return null;
+            }
+
             return New(driveInfo.Name);
         }
 

src/TestableIO.System.IO.Abstractions.TestingHelpers/MockFileSystemWatcherFactory.cs

@@ -43,6 +43,13 @@ public IFileSystemWatcher New(string path, string filter)
 
         /// <inheritdoc />
         public IFileSystemWatcher Wrap(FileSystemWatcher fileSystemWatcher)
-            => throw new NotImplementedException(StringResources.Manager.GetString("FILE_SYSTEM_WATCHER_NOT_IMPLEMENTED_EXCEPTION"));
+        {
+            if (fileSystemWatcher == null)
+            {
+                return null;
+            }
+
+            throw new NotImplementedException(StringResources.Manager.GetString("FILE_SYSTEM_WATCHER_NOT_IMPLEMENTED_EXCEPTION"));
+        }
     }
 }

src/TestableIO.System.IO.Abstractions.Wrappers/DriveInfoFactory.cs

@@ -38,6 +38,11 @@ public IDriveInfo New(string driveName)
         /// <inheritdoc />
         public IDriveInfo Wrap(DriveInfo driveInfo)
         {
+            if (driveInfo == null)
+            {
+                return null;
+            }
+
             return new DriveInfoWrapper(fileSystem, driveInfo);
         }
 

src/TestableIO.System.IO.Abstractions.Wrappers/FileSystemWatcherFactory.cs

@@ -42,6 +42,13 @@ public IFileSystemWatcher New(string path, string filter)
 
         /// <inheritdoc />
         public IFileSystemWatcher Wrap(FileSystemWatcher fileSystemWatcher)
-            => new FileSystemWatcherWrapper(FileSystem, fileSystemWatcher);
+        {
+            if (fileSystemWatcher == null)
+            {
+                return null;
+            }
+
+            return new FileSystemWatcherWrapper(FileSystem, fileSystemWatcher);
+        }
     }
 }

tests/TestableIO.System.IO.Abstractions.TestingHelpers.Tests/MockDriveInfoFactoryTests.cs

@@ -97,5 +97,15 @@ public void MockDriveInfoFactory_New_WithPathShouldReturnDrive()
             // Assert
             Assert.That(actualResult.Name, Is.EquivalentTo(@"Z:\"));
         }
+
+        [Test]
+        public void MockDriveInfoFactory_Wrap_WithNull_ShouldReturnNull()
+        {
+            var fileSystem = new MockFileSystem();
+
+            var result = fileSystem.DriveInfo.Wrap(null);
+
+            Assert.IsNull(result);
+        }
     }
 }

tests/TestableIO.System.IO.Abstractions.TestingHelpers.Tests/MockFileSystemWatcherFactoryTests.cs

@@ -37,5 +37,15 @@ public void MockFileSystemWatcherFactory_FromPath_ShouldThrowNotImplementedExcep
             var factory = new MockFileSystemWatcherFactory(new MockFileSystem());
             Assert.Throws<NotImplementedException>(() => factory.New(path));
         }
+
+        [Test]
+        public void MockFileSystemWatcherFactory_Wrap_WithNull_ShouldReturnNull()
+        {
+            var fileSystem = new MockFileSystem();
+
+            var result = fileSystem.FileSystemWatcher.Wrap(null);
+
+            Assert.IsNull(result);
+        }
     }
 }

tests/TestableIO.System.IO.Abstractions.Wrappers.Tests/DriveInfoFactoryTests.cs

@@ -0,0 +1,18 @@
+using NUnit.Framework;
+
+namespace System.IO.Abstractions.Tests
+{
+    [TestFixture]
+    public class DriveInfoFactoryTests
+    {
+        [Test]
+        public void Wrap_WithNull_ShouldReturnNull()
+        {
+            var fileSystem = new FileSystem();
+
+            var result = fileSystem.DriveInfo.Wrap(null);
+            
+            Assert.IsNull(result);
+        }
+    }
+}

tests/TestableIO.System.IO.Abstractions.Wrappers.Tests/FileSystemWatcherFactoryTests.cs

@@ -0,0 +1,18 @@
+using NUnit.Framework;
+
+namespace System.IO.Abstractions.Tests
+{
+    [TestFixture]
+    public class FileSystemWatcherFactoryTests
+    {
+        [Test]
+        public void Wrap_WithNull_ShouldReturnNull()
+        {
+            var fileSystem = new FileSystem();
+
+            var result = fileSystem.FileSystemWatcher.Wrap(null);
+            
+            Assert.IsNull(result);
+        }
+    }
+}