Unit-testing rendering views with Razor Engine not working in dotnet core 3.x

Describe the bug

Unit-testing rendering of Razor Views using Microsoft.AspNetCore.Mvc.Testing worked in dotnet core 2.2, but in 3.1 (and 3.0) the Razor Engine does not locate my views any more specified like this:

builder.UseSolutionRelativeContentRoot("Rendering");

To Reproduce

I have made a small example that reproduces the issue in the dotnet core 3.1 solution (while in the dotnet core 2.2 solution the view is found).

https://github.com/toralux/RazorEngineRendering

• dotnetcore3.1
• dotnetcore2.2

The only difference between the solutions is the framework (TargetFramework is netcoreapp3.1 instead of netcoreapp2.2) and version of nuget packages (Microsoft.AspNetCore.Mvc and Microsoft.AspNetCore.Mvc.Testing) (version 3.1.0 instead of 2.2.0).

The part of the example that don’t find the view:

var viewEngineResult = _viewEngine.FindView(actionContext, name, false);

if (!viewEngineResult.Success) // <-- here 2.2 has found the view and 3.1 has not
{
    throw new InvalidOperationException(string.Format("Couldn't find view '{0}'", name));
}

Further technical details

• ASP.NET Core version: 3.1 (and 3.0)

[brockallen]

I tried this and now it seems to be working:

            var builder = new WebHostBuilder();
            builder.ConfigureAppConfiguration((context, b) => {
                context.HostingEnvironment.ApplicationName = typeof(HomeController).Assembly.GetName().Name;
            });

Makes me wonder why it worked in 2.1.

[brockallen]

Setting an explicit content root via UseContentRoot also has no effect.