mock-servlet.groovy

def servlet = [
        doPost : {req, res ->
            println 'hello servlet'
        }
] as javax.servlet.http.HttpServlet

def req = [
        getProtocol : {'HTTP/1.1'}
] as javax.servlet.http.HttpServletRequest

def res = [
        sendError : {code, msg ->
            println "$code : $msg"
        }
] as javax.servlet.http.HttpServletResponse

servlet.doGet(req, res)
servlet.doPost(req, res)

result.txt

405 : HTTPのGETメソッドは、このURLではサポートされていません。
hello servlet