CompilationFailedException during runtime compilation of Razor from AspNetCore TestHost

Question

I have ASP.Net MVC application, one part of it is compiling razor views to string. The code is very similar to this example: https://long2know.com/2017/08/rendering-and-emailing-embedded-razor-views-with-net-core/

I registered Razor engine in Startup.cs in this way:

var viewAssembly = typeof(HtmlGeneratorService).GetTypeInfo().Assembly;
var fileProvider = new EmbeddedFileProvider(
    viewAssembly,
    "ApplicationServices.Widgets.Html.Templates");

services.Configure<MvcRazorRuntimeCompilationOptions>(options => {
    options.FileProviders.Clear();
    options.FileProviders.Add(fileProvider);
});

services.AddRazorPages().AddRazorRuntimeCompilation();

In test project i have this setup:

var builder = new HostBuilder()
    .ConfigureWebHost(webHost =>
    {
        webHost.UseTestServer();
        webHost.UseStartup<Startup>();
    });

var host = await builder.StartAsync();

HttpClient = host.GetTestClient();

But when i call my endpoint using this HttpClient, IRazorViewEngine.GetView starts to throw strange exceptions:

Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation.CompilationFailedException: 'One or more compilation failures occurred:
rnouw0xu.21w(4,41): error CS0234: The type or namespace name 'Razor' does not exist in the namespace 'Microsoft.AspNetCore' (are you missing an assembly reference?)
rnouw0xu.21w(4,82): error CS0518: Predefined type 'System.Type' is not defined or imported
rnouw0xu.21w(4,110): error CS0518: Predefined type 'System.String' is not defined or imported
rnouw0xu.21w(4,127): error CS0518: Predefined type 'System.String' is not defined or imported
rnouw0xu.21w(8,11): error CS0246: The type or namespace name 'System' could not be found (are you missing a using directive or an assembly reference?)
rnouw0xu.21w(9,11): error CS0246: The type or namespace name 'System' could not be found (are you missing a using directive or an assembly reference?)
rnouw0xu.21w(10,11): error CS0246: The type or namespace name 'System' could not be found (are you missing a using directive or an assembly reference?)
rnouw0xu.21w(11,11): error CS0246: The type or namespace name 'System' could not be found (are you missing a using directive or an assembly reference?)
rnouw0xu.21w(13,36): error CS0234: The type or namespace name 'Rendering' does not exist in the namespace 'Microsoft.AspNetCore.Mvc' (are you missing an assembly reference?)
rnouw0xu.21w(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?)
rnouw0xu.21w(29,35): error CS0234: The type or namespace name 'Razor' does not exist in the namespace 'Microsoft.AspNetCore' (are you missing an assembly reference?)
rnouw0xu.21w(29,78): error CS0518: Predefined type 'System.String' is not defined or imported
rnouw0xu.21w(29,87): error CS0518: Predefined type 'System.String' is not defined or imported

I trided to fix this erros in many different ways bul it looks like I got stuck here.

Answer 1

Looks like i found answer in this article: https://github.com/aspnet/Razor/issues/1212

I just added this code to my test.csproj file:

<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)')" />