Adding an assembly resolver which returns the already loaded assembly.

src/VisualStudio/TestUtilities/VisualStudioInstanceFactory.cs

@@ -28,6 +28,24 @@ static VisualStudioInstanceFactory()
             {
                 throw new PlatformNotSupportedException("The Visual Studio Integration Test Framework is only supported on Visual Studio 15.0 and later.");
             }
+
+            // This looks like it is pointless (since we are returning an assembly that is already loaded) but it is actually required.
+            // The BinaryFormatter, when invoking 'HandleReturnMessage', will end up attempting to call 'BinaryAssemblyInfo.GetAssembly()',
+            // which will itself attempt to call 'Assembly.Load()' using the full name of the assembly for the type that is being deserialized.
+            // Depending on the manner in which the assembly was originally loaded, this may end up actually trying to load the assembly a second
+            // time and it can fail if the standard assembly resolution logic fails. This ensures that we 'succeed' this secondary load by returning
+            // the assembly that is already loaded.
+            AppDomain.CurrentDomain.AssemblyResolve += (sender, eventArgs) => { 
+                Debug.WriteLine($"'{eventArgs.RequestingAssembly}' is attempting to resolve '{eventArgs.Name}'");
+                var resolvedAssembly = AppDomain.CurrentDomain.GetAssemblies().Where((assembly) => assembly.FullName.Equals(eventArgs.Name)).SingleOrDefault();
+
+                if (resolvedAssembly != null)
+                {
+                    Debug.WriteLine("The assembly was already loaded!");
+                }
+
+                return resolvedAssembly;
+            };
         }
 
         /// <summary>