You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: iterator_test.go
    path of file: ./repos/go-ethereum/core/state
    
    the code of the file until where you have to start completion: // Copyright 2016 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

package state
    
func testNodeIteratorCoverage(t *testing.T, scheme string) {
	// Create some arbitrary test state to iterate
	db, sdb, ndb, root, _ := makeTestState(scheme)
	ndb.Commit(root, false)

	state, err := New(root, sdb, nil)
	if err != nil {
		t.Fatalf("failed to create state trie at %x: %v", root, err)
	}
	// Gather all the node hashes found by the iterator
	hashes := make(map[common.Hash]struct{})
	for it := newNodeIterator(state); it.Next(); {
		if it.Hash != (common.Hash{}) {
			hashes[it.Hash] = struct{}{}
		}
	}
	// Check in-disk nodes
	var (
		seenNodes = make(map[common.Hash]struct{})
		seenCodes = make(map[common.Hash]struct{})
	)
	it := db.NewIterator(nil, nil)
	for it.Next() {
		ok, hash := isTrieNode(scheme, it.Key(), it.Value())
		if !ok {
			continue
		}
		seenNodes[hash] = struct{}{}
	}
	it.Release()

	// Check in-disk codes
	it = db.NewIterator(nil, nil)
	for it.Next() {
		ok, hash := rawdb.IsCodeKey(it.Key())
		if !ok {
			continue
		}
		if _, ok := hashes[common.BytesToHash(hash)]; !ok {
			t.Errorf("state entry not reported %x", it.Key())
		}
		seenCodes[common.BytesToHash(hash)] = struct{}{}
	}
	it.Release()

	// Cross check the iterated hashes and the database/nodepool content
	for hash := range hashes {
		_, ok := seenNodes[hash]
		if !ok {
			_, ok = seenCodes[hash]
		}
		if !ok {
			t.Errorf("failed to retrieve reported node %x", hash)
		}
	}
}