Rely on AppContext.BaseDirectory as content root, rather than trying to get assume the path based on the solution folder, which doesn't work for many customers.

Author: mkArtakMSFT

src/Mvc/Mvc.Testing/src/WebApplicationFactory.cs

@@ -246,16 +246,28 @@ private void SetContentRoot(IWebHostBuilder builder)
             return;
         }
 
-        var fromFile = File.Exists("MvcTestingAppManifest.json");
-        var contentRoot = fromFile ? GetContentRootFromFile("MvcTestingAppManifest.json") : GetContentRootFromAssembly();
+        string? contentRoot = null;
+        if (File.Exists("MvcTestingAppManifest.json"))
+        {
+            var manifestContentRoot = GetContentRootFromFile("MvcTestingAppManifest.json");
+            if (manifestContentRoot is not null && Directory.Exists(manifestContentRoot))
+            {
+                contentRoot = manifestContentRoot;
+            }
+        }
+
+        if (contentRoot is null)
+        {
+            contentRoot = GetContentRootFromAssembly();
+        }
 
-        if (contentRoot != null && Directory.Exists(contentRoot))
+        if (contentRoot is not null && Directory.Exists(contentRoot))
         {
             builder.UseContentRoot(contentRoot);
         }
         else
         {
-            builder.UseSolutionRelativeContentRoot(typeof(TEntryPoint).Assembly.GetName().Name!);
+            builder.UseContentRoot(AppContext.BaseDirectory);
         }
     }