#4 Fix using replacement

Author: inyutin-maxim

System.IO.Abstractions.Analyzers.Tests/TestData/CodeFix/FileServiceConstructorInitialCodeFix/AfterFix.txt

@@ -1,3 +1,4 @@
+using System.IO;
 using System.IO.Abstractions;
 
 namespace SomeNameSpace

System.IO.Abstractions.Analyzers/CodeActions/FileServiceConstructorInitialCodeAction.cs

@@ -48,10 +48,27 @@ protected override async Task<Document> GetChangedDocumentAsync(CancellationToke
 
 			var compilationUnitSyntax = RoslynClassFileSystem.GetCompilationUnit(_class);
 
-			if (compilationUnitSyntax.Usings.Any())
+			if (!compilationUnitSyntax.Usings.Any())
 			{
-				editor.ReplaceNode(RoslynClassFileSystem.GetSystemIoUsing(compilationUnitSyntax),
+				return editor.GetChangedDocument();
+			}
+
+			var fileSystem = RoslynClassFileSystem.GetUsing(compilationUnitSyntax, Constants.FileSystemNameSpace);
+
+			if (fileSystem != default(UsingDirectiveSyntax))
+			{
+				return editor.GetChangedDocument();
+			}
+
+			var systemIo = RoslynClassFileSystem.GetSystemIoUsing(compilationUnitSyntax);
+
+			if (systemIo == default(UsingDirectiveSyntax))
+			{
+				editor.InsertBefore(compilationUnitSyntax.Usings.FirstOrDefault(),
 					RoslynClassFileSystem.GetFileSystemUsing());
+			} else
+			{
+				editor.InsertAfter(systemIo, RoslynClassFileSystem.GetFileSystemUsing());
 			}
 
 			return editor.GetChangedDocument();

System.IO.Abstractions.Analyzers/CodeActions/FileServiceInterfaceInjectionCodeAction.cs

@@ -68,8 +68,7 @@ protected override async Task<Document> GetChangedDocumentAsync(CancellationToke
 					RoslynClassFileSystem.GetFileSystemUsing());
 			} else
 			{
-				editor.InsertAfter(compilationUnitSyntax.Usings.FirstOrDefault(),
-					RoslynClassFileSystem.GetFileSystemUsing());
+				editor.InsertAfter(systemIo, RoslynClassFileSystem.GetFileSystemUsing());
 			}
 
 			return editor.GetChangedDocument();