WebApplicationFactory throws error that contentRootPath does not exist in ASP.NET Core integration test

I have a ASP.NET Core project with some simple Razor pages and a Web API controller.

I'm using Clean Architecture as a starting point. I've renamed the project names, removed the MVC stuff and added some of my own code. Everything runs and works.

However, the integration tests throw the following error when calling factory.CreateClient():

Test Name:  ToDo.Tests.Integration.Web.HomeControllerIndexShould.ReturnViewWithCorrectMessage
Test FullName:  ToDo.Tests.Integration.Web.HomeControllerIndexShould.ReturnViewWithCorrectMessage
Test Source:    C:\Source\Utopia\tests\ToDo.Tests\Integration\Web\HomeControllerIndexShould.cs : line 18
Test Outcome:   Failed
Test Duration:  0:00:00,001

Result StackTrace:  
at Microsoft.AspNetCore.Hosting.Internal.HostingEnvironmentExtensions.Initialize(IHostingEnvironment hostingEnvironment, String contentRootPath, WebHostOptions options)
   at Microsoft.AspNetCore.Hosting.WebHostBuilder.BuildCommonServices(AggregateException& hostingStartupErrors)
   at Microsoft.AspNetCore.Hosting.WebHostBuilder.Build()
   at Microsoft.AspNetCore.TestHost.TestServer..ctor(IWebHostBuilder builder, IFeatureCollection featureCollection)
   at Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory`1.CreateServer(IWebHostBuilder builder)
   at Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory`1.EnsureServer()
   at Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory`1.CreateDefaultClient(DelegatingHandler[] handlers)
   at Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory`1.CreateClient(WebApplicationFactoryClientOptions options)
   at ToDo.Tests.Integration.Web.HomeControllerIndexShould..ctor(CustomWebApplicationFactory`1 factory) in C:\Source\Utopia\tests\ToDo.Tests\Integration\Web\HomeControllerIndexShould.cs:line 14
Result Message: 
System.ArgumentException : The content root 'C:\Source\Utopia\ToDo.Web' does not exist.
Parameter name: contentRootPath

I've tried configuring the custom WebApplicationFactory by using builder.UseContentRoot and builder.UseSolutionRelativeContentRoot but it keeps throwing the same error no matter what values I use for the ContentRoot methods.

I don't know why my tests are failing while the one in the Clean Architecture sample are working. I also don't know how to fix it.

Any pointers are highly appreciated!

Solution

This method worked for me

var client = _factory
    .WithWebHostBuilder(builder => builder.UseSolutionRelativeContentRoot("relative/path/of/project/under/test"))
    .CreateClient();

How the test infrastructure infers the app content root path says (with my markup added)

The WebApplicationFactory constructor infers the app content root path by searching for a WebApplicationFactoryContentRootAttribute on the assembly containing the integration tests with a key equal to the TEntryPoint assembly System.Reflection.Assembly.FullName. In case an attribute with the correct key isn't found, WebApplicationFactory falls back to searching for a solution file (.sln) and appends the TEntryPoint assembly name to the solution directory. The app root directory (the content root path) is used to discover views and content files.