How to solve !action_type.empty(): Unknown action hi in contract hello?

Question

I am following this doc: https://developers.eos.io/eosio-home/docs/your-first-contract.

This is the hello.cpp contract code which is successfully deployed:

#include <eosiolib/eosio.hpp>
#include <eosiolib/print.hpp>
using namespace eosio;

class hello : public contract {
  public:
      using contract::contract;

      [[eosio::action]]
      void testit( name user ) {
         print( "Hello, ", name{user});
      }
};
EOSIO_DISPATCH( hello, (testit))

When I call cleos push action hello testit '[]' -p hello@active, this error is shown on the console:

!action_type.empty(): Unknown action testit in contract hello