The type 'Attribute' is defined in an assembly that is not referenced.

[Nathan-Ryan]

I'm encountering this error when using MSTest and the Microsoft.AspNetCore.TestHost. It all works fine until I call the TestServer to render a view.

I'm using VS2017 15.3 with the .NET Core 2.0 Sdk with my net.core app targeting .NET Framework 4.6.1.
Any advise on how I might fix this?

"Microsoft.AspNetCore.Mvc.Razor.Compilation.CompilationFailedException: One or more compilation failures occurred:\r\ne3s05cht.itf(4,62): error CS0012: The type 'Attribute' is defined in an assembly that is not referenced. You must add a reference to assembly 'netstandard, Version=2.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51'.\r\ne3s05cht.itf(4,81): error CS0518: Predefined type 'System.String' is not defined or imported\r\ne3s05cht.itf(4,109): error CS0518: Predefined type 'System.Type' is not defined or imported\r\ne3s05cht.itf(4,11): error CS0518: Predefined type 'System.Void' is not defined or imported\r\ne3s05cht.itf(8,11): error CS0246: The type or namespace name 'System' could not be found (are you missing a using directive or an assembly reference?)\r\ne3s05cht.itf(9,11): error CS0246: The type or namespace name 'System' could not be found (are you missing a using directive or an assembly reference?)\r\ne3s05cht.itf(10,11): error CS0246: The type or namespace name 'System' could not be fou
nd (are you missing a using directive or an assembly reference?)\r\ne3s05cht.itf(11,11): error CS0246: The type or namespace name 'System' could not be found (are you missing a using directive or an assembly reference?)\r\ne3s05cht.itf(14,36): error CS0234: The type or namespace name 'ViewFeatures' does not exist in the namespace 'Microsoft.AspNetCore.Mvc' (are you missing an assembly reference?)\r\ne3s05cht.itf(15,93): error CS1980: Cannot define a class or member that utilizes 'dynamic' because the compiler required type 'System.Runtime.CompilerServices.DynamicAttribute' cannot be found. Are you missing a reference?\r\ne3s05cht.itf(15,93): error CS0518: Predefined type 'System.Boolean' is not defined or imported\r\ne3s05cht.itf(15,44): error CS0012: The type 'Object' is defined in an assembly that is not referenced. You must add a reference to assembly 'netstandard, Version=2.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51'.\r\ne3s05cht.itf(18,67): error CS1983: The return type of an async method mus
t be void, Task or Task<T>\r\ne3s05cht.itf(18,39): error CS0400: The type or namespace name 'System' could not be found in the global namespace (are you missing an assembly reference?)\r\ne3s05cht.itf(70,49): error CS0234: The type or namespace name 'ViewFeatures' does not exist in the namespace 'Microsoft.AspNetCore.Mvc' (are you missing an assembly reference?)\r\ne3s05cht.itf(70,118): error CS0518: Predefined type 'System.Void' is not defined or imported\r\ne3s05cht.itf(72,49): error CS0234: The type or namespace name 'IUrlHelper' does not exist in the namespace 'Microsoft.AspNetCore.Mvc' (are you missing an assembly reference?)\r\ne3s05cht.itf(72,71): error CS0518: Predefined type 'System.Void' is not defined or imported\r\ne3s05cht.itf(74,49): error CS0234: The type or namespace name 'IViewComponentHelper' does not exist in the namespace 'Microsoft.AspNetCore.Mvc' (are you missing an assembly reference?)\r\ne3s05cht.itf(74,87): error CS0518: Predefined type 'System.Void' is not defined or imported\r\ne3s05
cht.itf(76,59): error CS0234: The type or namespace name 'IJsonHelper' does not exist in the namespace 'Microsoft.AspNetCore.Mvc.Rendering' (are you missing an assembly reference?)\r\ne3s05cht.itf(76,83): error CS0518: Predefined type 'System.Void' is not defined or imported\r\ne3s05cht.itf(78,59): error CS0234: The type or namespace name 'IHtmlHelper<>' does not exist in the namespace 'Microsoft.AspNetCore.Mvc.Rendering' (are you missing an assembly reference?)\r\ne3s05cht.itf(78,71): error CS0012: The type 'Object' is defined in an assembly that is not referenced. You must add a reference to assembly 'netstandard, Version=2.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51'.\r\ne3s05cht.itf(78,71): error CS0518: Predefined type 'System.Object' is not defined or imported\r\ne3s05cht.itf(78,71): error CS1980: Cannot define a class or member that utilizes 'dynamic' because the compiler required type 'System.Runtime.CompilerServices.DynamicAttribute' cannot be found. Are you missing a reference?\r\ne3s05ch
t.itf(78,71): error CS0518: Predefined type 'System.Boolean' is not defined or imported\r\ne3s05cht.itf(78,92): error CS0518: Predefined type 'System.Void' is not defined or imported\r\ne3s05cht.itf(18,67): error CS0508: '_Views_PublicApp_cshtml.ExecuteAsync()': return type must be 'Task' to match overridden member 'RazorPageBase.ExecuteAsync()'\r\ne3s05cht.itf(18,67): error CS0012: The type 'Task' is defined in an assembly that is not referenced. You must add a reference to assembly 'netstandard, Version=2.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51'.\r\ne3s05cht.itf(69,58): error CS0012: The type 'Attribute' is defined in an assembly that is not referenced. You must add a reference to assembly 'netstandard, Version=2.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51'.\r\ne3s05cht.itf(69,10): error CS0518: Predefined type 'System.Void' is not defined or imported\r\ne3s05cht.itf(71,58): error CS0012: The type 'Attribute' is defined in an assembly that is not referenced. You must add a referen
ce to assembly 'netstandard, Version=2.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51'.\r\ne3s05cht.itf(71,10): error CS0518: Predefined type 'System.Void' is not defined or imported\r\ne3s05cht.itf(73,58): error CS0012: The type 'Attribute' is defined in an assembly that is not referenced. You must add a reference to assembly 'netstandard, Version=2.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51'.\r\ne3s05cht.itf(73,10): error CS0518: Predefined type 'System.Void' is not defined or imported\r\ne3s05cht.itf(75,58): error CS0012: The type 'Attribute' is defined in an assembly that is not referenced. You must add a reference to assembly 'netstandard, Version=2.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51'.\r\ne3s05cht.itf(75,10): error CS0518: Predefined type 'System.Void' is not defined or imported\r\ne3s05cht.itf(77,58): error CS0012: The type 'Attribute' is defined in an assembly that is not referenced. You must add a reference to assembly 'netstandard, Version=2.0.0.0, Culture=ne
utral, PublicKeyToken=cc7b13ffcd2ddd51'.\r\ne3s05cht.itf(77,10): error CS0518: Predefined type 'System.Void' is not defined or imported\r\ne3s05cht.itf(20,13): error CS0012: The type 'Object' is defined in an assembly that is not referenced. You must add a reference to assembly 'netstandard, Version=2.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51'.\r\ne3s05cht.itf(20,13): error CS0518: Predefined type 'System.Object' is not defined or imported\r\ne3s05cht.itf(20,26): error CS0518: Predefined type 'System.Int32' is not defined or imported\r\ne3s05cht.itf(20,29): error CS0518: Predefined type 'System.Int32' is not defined or imported\r\ne3s05cht.itf(20,34): error CS0518: Predefined type 'System.Boolean' is not defined or imported\r\ne3s05cht.itf(20,13): error CS0518: Predefined type 'System.Void' is not defined or imported\r\ne3s05cht.itf(21,13): error CS0012: The type 'Object' is defined in an assembly that is not referenced. You must add a reference to assembly 'netstandard, Version=2.0.0.0, Culture=
neutral, PublicKeyToken=cc7b13ffcd2ddd51'.\r\ne3s05cht.itf(21,13): error CS0518: Predefined type 'System.Object' is not defined or imported\r\ne3s05cht.itf(21,26): error CS0518: Predefined type 'System.String' is not defined or imported\r\ne3s05cht.itf(21,13): error CS0518: Predefined type 'System.Void' is not defined or imported\r\ne3s05cht.itf(36,13): error CS0012: The type 'Object' is defined in an assembly that is not referenced. You must add a reference to assembly 'netstandard, Version=2.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51'.\r\ne3s05cht.itf(36,13): error CS0518: Predefined type 'System.Object' is not defined or imported\r\ne3s05cht.itf(36,13): error CS0518: Predefined type 'System.Void' is not defined or imported\r\ne3s05cht.itf(43,13): error CS0012: The type 'Object' is defined in an assembly that is not referenced. You must add a reference to assembly 'netstandard, Version=2.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51'.\r\ne3s05cht.itf(43,13): error CS0518: Predefined ty
pe 'System.Object' is not defined or imported\r\ne3s05cht.itf(43,26): error CS0518: Predefined type 'System.Int32' is not defined or imported\r\ne3s05cht.itf(43,31): error CS0518: Predefined type 'System.Int32' is not defined or imported\r\ne3s05cht.itf(43,36): error CS0518: Predefined type 'System.Boolean' is not defined or imported\r\ne3s05cht.itf(43,13): error CS0518: Predefined type 'System.Void' is not defined or imported\r\ne3s05cht.itf(44,13): error CS0012: The type 'Object' is defined in an assembly that is not referenced. You must add a reference to assembly 'netstandard, Version=2.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51'.\r\ne3s05cht.itf(44,13): error CS0518: Predefined type 'System.Object' is not defined or imported\r\ne3s05cht.itf(44,26): error CS0518: Predefined type 'System.String' is not defined or imported\r\ne3s05cht.itf(44,13): error CS0518: Predefined type 'System.Void' is not defined or imported\r\ne3s05cht.itf(48,13): error CS0012: The type 'Object' is defined in an assembl
y that is not referenced. You must add a reference to assembly 'netstandard, Version=2.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51'.\r\ne3s05cht.itf(48,13): error CS0518: Predefined type 'System.Object' is not defined or imported\r\ne3s05cht.itf(48,13): error CS0518: Predefined type 'System.Void' is not defined or imported\r\ne3s05cht.itf(56,13): error CS0012: The type 'Object' is defined in an assembly that is not referenced. You must add a reference to assembly 'netstandard, Version=2.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51'.\r\ne3s05cht.itf(56,13): error CS0518: Predefined type 'System.Object' is not defined or imported\r\ne3s05cht.itf(56,26): error CS0518: Predefined type 'System.Int32' is not defined or imported\r\ne3s05cht.itf(56,31): error CS0518: Predefined type 'System.Int32' is not defined or imported\r\ne3s05cht.itf(56,36): error CS0518: Predefined type 'System.Boolean' is not defined or imported\r\ne3s05cht.itf(56,13): error CS0518: Predefined type 'System.Void' is not d
efined or imported\r\ne3s05cht.itf(57,13): error CS0012: The type 'Object' is defined in an assembly that is not referenced. You must add a reference to assembly 'netstandard, Version=2.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51'.\r\ne3s05cht.itf(57,13): error CS0518: Predefined type 'System.Object' is not defined or imported\r\ne3s05cht.itf(57,26): error CS0518: Predefined type 'System.String' is not defined or imported\r\ne3s05cht.itf(57,13): error CS0518: Predefined type 'System.Void' is not defined or imported\r\ne3s05cht.itf(58,13): error CS0012: The type 'Object' is defined in an assembly that is not referenced. You must add a reference to assembly 'netstandard, Version=2.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51'.\r\ne3s05cht.itf(58,13): error CS0518: Predefined type 'System.Object' is not defined or imported\r\ne3s05cht.itf(58,13): error CS0518: Predefined type 'System.Void' is not defined or imported\r\ne3s05cht.itf(64,13): error CS0012: The type 'Object' is defined in an as
sembly that is not referenced. You must add a reference to assembly 'netstandard, Version=2.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51'.\r\ne3s05cht.itf(64,13): error CS0518: Predefined type 'System.Object' is not defined or imported\r\ne3s05cht.itf(64,26): error CS0518: Predefined type 'System.Int32' is not defined or imported\r\ne3s05cht.itf(64,32): error CS0518: Predefined type 'System.Int32' is not defined or imported\r\ne3s05cht.itf(64,37): error CS0518: Predefined type 'System.Boolean' is not defined or imported\r\ne3s05cht.itf(64,13): error CS0518: Predefined type 'System.Void' is not defined or imported\r\ne3s05cht.itf(65,13): error CS0012: The type 'Object' is defined in an assembly that is not referenced. You must add a reference to assembly 'netstandard, Version=2.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51'.\r\ne3s05cht.itf(65,13): error CS0518: Predefined type 'System.Object' is not defined or imported\r\ne3s05cht.itf(65,26): error CS0518: Predefined type 'System.String' i
s not defined or imported\r\ne3s05cht.itf(65,13): error CS0518: Predefined type 'System.Void' is not defined or imported\r\ne3s05cht.itf(66,13): error CS0012: The type 'Object' is defined in an assembly that is not referenced. You must add a reference to assembly 'netstandard, Version=2.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51'.\r\ne3s05cht.itf(66,13): error CS0518: Predefined type 'System.Object' is not defined or imported\r\ne3s05cht.itf(66,13): error CS0518: Predefined type 'System.Void' is not defined or imported\r\ne3s05cht.itf(18,67): error CS0161: '_Views_PublicApp_cshtml.ExecuteAsync()': not all code paths return a value\r\ne3s05cht.itf(15,18): error CS0518: Predefined type 'System.Void' is not defined or imported\r\nC:\\Source\\TFS\\ReferenceApp\\RefApp.Web\\Views\\PublicApp.cshtml(15,10): error CS0518: Predefined type 'System.Boolean' is not defined or imported\r\n   at Microsoft.AspNetCore.Mvc.Razor.Internal.RazorViewCompiler.CompileAndEmit(RazorCodeDocument codeDocument, String gener
atedCode)\r\n   at Microsoft.AspNetCore.Mvc.Razor.Internal.RazorViewCompiler.CompileAndEmit(String relativePath)\r\n   at Microsoft.AspNetCore.Mvc.Razor.Internal.RazorViewCompiler.CreateCacheEntry(String normalizedPath)\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at Microsoft.AspNetCore.Mvc.Razor.Internal.DefaultRazorPageFactoryProvider.CreateFactory(String relativePath)\r\n   at Microsoft.AspNetCore.Mvc.Razor.RazorViewEngine.CreateCacheResult(HashSet`1 expirationTokens, String relativePath, Boolean isMainPage)\r\n   at Microsoft.AspNetCore.Mvc.Razor.RazorViewEngine.LocatePageFromPath(String executingFilePath, String pagePath, Boolean isMainPage)\r\n   at Microsoft.AspNetCore.Mvc.Razor.RazorViewEngine.GetView(String executingFilePath, String viewPath, Boolean isMainPage)\r\n   at Micro
soft.AspNetCore.Mvc.ViewEngines.CompositeViewEngine.GetView(String executingFilePath, String viewPath, Boolean isMainPage)\r\n   at Microsoft.AspNetCore.Mvc.ViewFeatures.Internal.ViewResultExecutor.FindView(ActionContext actionContext, ViewResult viewResult)\r\n   at Microsoft.AspNetCore.Mvc.ViewResult.<ExecuteResultAsync>d__26.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.<InvokeResultAsync>d__19.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at Microsoft.AspNetCore.Mvc.Internal.ResourceInvo
ker.<InvokeNextResultFilterAsync>d__24.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.Rethrow(ResultExecutedContext context)\r\n   at Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)\r\n   at Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.<InvokeNextResourceFilter>d__22.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.Rethrow(ResourceExecutedContext context)\r\n   at Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)\r\n   at Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.<InvokeFilterPipelineAsync>d__17.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task
 task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.<InvokeAsync>d__15.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at Microsoft.AspNetCore.Builder.RouterMiddleware.<Invoke>d__4.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd(Task task)\r\n   at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.<Invoke>d__6.MoveNext()\r\n--- End of stack trace from previous lo
cation where exception was thrown ---\r\n   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddleware.<Invoke>d__6.MoveNext()"

[pranavkm]

@Nathan-Ryan you might be running in to the same sort of issue as aspnet/Razor#1212. There's some guidance in aspnet/Razor#1212 (comment) for fixing this.

[Nathan-Ryan]

@pranavkm Sounds like it could be the same issue, although I'm using MSTest and not xUnit.
It does seem to be a problem with the dependencies of Razor. The tests for my API endpoints work as expected. Thanks for your help.

[pranavkm]

Perhaps DeploymentItem would help in this case?

[oferns]

I am having this issue as well. I am using MSTest and VS2017 15.3 with the .NET Core 2.0 Sdk with my net.core app targeting .NET Framework 4.6.1. I fixed it by adding this to the test project csproj

  <!--
    Work around https://github.com/NuGet/Home/issues/4412. MVC uses DependencyContext.Load()         which looks next to a .dll
    for a .deps.json. Information isn't available elsewhere. Need the .deps.json file for all web site     applications.
  -->
  <Target Name="CopyDepsFiles" AfterTargets="Build" Condition="'$(TargetFramework)'!=''">
    <ItemGroup>
      <DepsFilePaths Include="$([System.IO.Path]::ChangeExtension('%(_ResolvedProjectReferencePaths.FullPath)', '.deps.json'))" />
    </ItemGroup>

    <Copy SourceFiles="%(DepsFilePaths.FullPath)" DestinationFolder="$(OutputPath)" Condition="Exists('%(DepsFilePaths.FullPath)')" />
  </Target>

A

[pranavkm]

Microsoft.AspNetCore.Mvc.Testing takes care of copying the deps file from the application under test to the test app. See https://docs.microsoft.com/en-us/aspnet/core/test/integration-tests for specifics on how to set it up in your test applications.

[wtgodbe]

Closing as the discussion seems to be resolved