Add file headers in DocumentTransform tests

Author: amis92

src/CodeGeneration.Roslyn.Tests/DocumentTransformTests.cs

@@ -1,8 +1,6 @@
-using System.Collections.Generic;
-using System.Text;
-using System.Threading.Tasks;
-using Microsoft.Extensions.DependencyModel;
-using Validation;
+// Copyright (c) Andrew Arnott. All rights reserved.
+// Licensed under the MIT license. See LICENSE.txt file in the project root for full license information.
+
 using Xunit;
 
 public class DocumentTransformTests : CompilationTestsBase
@@ -326,4 +324,4 @@ partial struct Empty<T>
 }";
         AssertGeneratedAsExpected(source, generated);
     }
-}
+}

src/CodeGeneration.Roslyn.Tests/Helpers/CompilationTestsBase.cs

@@ -1,4 +1,7 @@
-using System;
+// Copyright (c) Andrew Arnott. All rights reserved.
+// Licensed under the MIT license. See LICENSE.txt file in the project root for full license information.
+
+using System;
 using System.Collections.Immutable;
 using System.IO;
 using System.Linq;
@@ -94,4 +97,4 @@ protected static Project CreateProject(params string[] sources)
         }
         return solution.GetProject(projectId);
     }
-}
+}