ArgumentNullException when performing AspNetCore Integration Tests using `Microsoft.AspNetCore.TestHost.TestServer`

Describe the bug ArgumentNullException when performing AspNetCore Integration Tests using Microsoft.AspNetCore.TestHost.TestServer

Value cannot be null.
Parameter name: operatingAssembly (See inner exception for details.) ---> 
System.ArgumentNullException: Value cannot be null.
Parameter name: operatingAssembly
   
at RazorLight.Compilation.RoslynCompilationService..ctor(IMetadataReferenceManager referenceManager, Assembly operatingAssembly)
   
at RazorLight.RazorLightEngineBuilder.Build()
   
at Services.Contract.IoC.ContractDomainModule.<>c.<Load>b__0_0(IComponentContext x)
   

To reproduce: Run a test class library targeting .NET Framework 4.7.1. but running a .NETCore api. Inject the RazorlightEngine in a controller, query the controller end point and wait for it to throw.

Information (please complete the following information):

• OS: Windows 10
• Platform .NET Framework 4.x
• RazorLight version: 2.0.0-beta1

[talanc]

I’m getting the same exception in a .NET Framework 4.6.1 MSTest project – but not when I’m running the ASP.NET Core project…

operatingAssembly must be null from a test project?

[BarsikV]

I have a .netframework project and I had a similar issue. You need to call “SetOperatingAssembly” and pass the assembly where you actually use the razor engine. To make this work I created a factory that is easily injectable and it can create the razor engine wherever and whenever I need it. Example of the factory:

public class RazorEngineFactory : IRazorEngineFactory
{
    public IRazorLightEngine Create()
    {
        return new RazorLightEngineBuilder()
            .SetOperatingAssembly(Assembly.GetCallingAssembly())
            .UseFileSystemProject(Directory.GetCurrentDirectory())
            .UseMemoryCachingProvider()
            .Build();
    }
}

Just inject this factory and use it to create the razor engine instead of directly injecting the engine. By the way, i am using the filesystem resource type, just change it to embedded as you need.