fix: Refresh FileInfo & DirectoryInfo after adding to MockFileSystem

Modify the `IFileInfo` and `IDirectoryInfo` overloads of `AddFile()`,
`AddEmptyFile()`, or `AddDirectory()` in `MockFileSystem`, to call
`Refresh()` on those objects after the paths they refer to are created.

Author: rcdailey

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

@@ -225,6 +225,7 @@ public void AddEmptyFile(string path)
         public void AddEmptyFile(IFileInfo path)
         {
             AddEmptyFile(path.FullName);
+            path.Refresh();
         }
 
         /// <summary>
@@ -234,6 +235,7 @@ public void AddEmptyFile(IFileInfo path)
         public void AddDirectory(IDirectoryInfo path)
         {
             AddDirectory(path.FullName);
+            path.Refresh();
         }
 
         /// <summary>
@@ -244,6 +246,7 @@ public void AddDirectory(IDirectoryInfo path)
         public void AddFile(IFileInfo path, MockFileData data)
         {
             AddFile(path.FullName, data);
+            path.Refresh();
         }
 
         /// <summary>

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

@@ -130,6 +130,39 @@ public void MockFileSystem_AddEmptyFile_ShouldBeEmpty()
             Assert.That(fileSystem.GetFile(path).TextContents, Is.EqualTo(""));
         }
 
+        [Test]
+        public void MockFileSystem_AddEmptyFile_ShouldExist()
+        {
+            var fileSystem = new MockFileSystem();
+            var path = fileSystem.FileInfo.New(XFS.Path(@"c:\some\file.txt"));
+
+            fileSystem.AddEmptyFile(path);
+
+            Assert.That(path.Exists, Is.True);
+        }
+
+        [Test]
+        public void MockFileSystem_AddFile_ShouldExist()
+        {
+            var fileSystem = new MockFileSystem();
+            var path = fileSystem.FileInfo.New(XFS.Path(@"c:\some\file.txt"));
+
+            fileSystem.AddFile(path, new MockFileData("stuff"));
+
+            Assert.That(path.Exists, Is.True);
+        }
+
+        [Test]
+        public void MockFileSystem_AddDirectory_ShouldExist()
+        {
+            var fileSystem = new MockFileSystem();
+            var path = fileSystem.DirectoryInfo.New(XFS.Path(@"c:\thedir"));
+
+            fileSystem.AddDirectory(path);
+
+            Assert.That(path.Exists, Is.True);
+        }
+
         [Test]
         public void MockFileSystem_ByDefault_IsSerializable()
         {