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: gen_test.go
    path of file: ./repos/gonum/graph/graphs/gen
    
    the code of the file until where you have to start completion: // Copyright Â©2021 The Gonum Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package gen

import (
	"bytes"
	"fmt"
	"testing"

	"gonum.org/v1/gonum/graph"
	"gonum.org/v1/gonum/graph/encoding/dot"
	"gonum.org/v1/gonum/graph/simple"
)

type nodeIDGraphBuilder interface {
	graph.Graph
	NodeIDGraphBuilder
}

func undirected() nodeIDGraphBuilder { retur
    
func TestCheck(t *testing.T) {
	tests := []struct {
		ids   IDer
		extra []int64
		want  string
	}{
		{
			ids: IDSet{1, 2, 3, 4}, extra: []int64{1},
			want: "gen: node ID collision i=0 with extra: id=1",
		},
		{
			ids: IDSet{1, 2, 3, 4}, extra: []int64{5, 2},
			want: "gen: node ID collision i=1 with extra j=1: id=2",
		},
		{
			ids: IDSet{}, extra: []int64{1, 2, 1},
			want: "gen: extra node ID collision i=0 j=2: id=1",
		},
	}

	for _, test := range tests {
		msg := fmt.Sprint(check(test.ids, test.extra...))
		if msg != test.want {
			t.Errorf("unexpected check panic for ids=%#v extra=%v: got:%q want:%q",
				test.ids, test.extra, msg, test.want)
		}
	}
}