Episerver.Marketing.Testing makes our WebApi routes return 500 errors

Hi,

We installed the latest version of Episerver.Marketing.Testing, 2.5.5 in our solution and now our webapi routes don't work anymore. We get the following error on all our webapi routes: 

ExceptionMessage: "The object has not yet been initialized. Ensure that HttpConfiguration.EnsureInitialized() is called in the application's startup code after all other initialization code."

Before installing the package everything worked fine. I think it has to do with how the plugin initializes its own routes and does it in a way that we can't add our own.

Any thoughts?