Testing Guice can init servlets

Sequel to the prev post, binding servlets is not enough. You must make sure that Guice can initiate them. For example, a common error is not binding servlets as singleton, there you get exceptions like

ServletException: Servlets must be bound as singletons. Key[type=my.servlet.FooServlet, annotation=[none]] was not bound in singleton scope.

Here's a way to test for all servlets in Guice context When calling init on the filter it would init all servlets in context.