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: tailnet_test.go
    path of file: ./repos/coder/coderd
    
    the code of the file until where you have to start completion: package coderd_test

import (
	"context"
	"fmt"
	"io"
	"net"
	"net/http"
	"net/http/httptest"
	"net/url"
	"strconv"
	"sync/atomic"
	"testing"

	"github.com/google/uuid"
	"github.com/prometheus/client_golang/prometheus"
	"github.com/spf13/afero"
	"github.com/stretchr/testify/assert"
	"github.com/stretchr/testify/require"
	"go.opentelemetry.io/otel/trace"
	"tailscale.com/tailcfg"

	"cdr.dev/slog"
	"cdr.dev/slog/sloggers/slogtest"
	"github.com/coder/coder/v2/agent"
	"github.com/coder/coder/v2/agent/agenttest"
	"github.com/coder/coder/v2/agent/proto"
	"github.com/coder/coder/v2/coderd"
	"github.com/coder/coder/v2/codersdk"
	"github.com/coder/coder/v2/codersdk/agentsdk"
	"github.com/coder/coder/v2/tailnet"
	"github.com/coder/coder/v2/tailnet/tailnettest"
	"github.com/coder/coder/v2/testutil"
)

func TestServerTailnet_AgentConn_OK(t *testing.T) {
	t.Parallel()

	ctx, cancel := context.WithTimeout(context.Background(), testutil.WaitMedium)
	defer cancel()

	// Connect through the ServerTailnet
	agents, serverTailnet := setupServerTailnetAgent(t, 1)
	a := agents[0]

	conn, release, err := serverTailnet.AgentConn(ctx, a.id)
	req
    
func setupServerTailnetAgent(t *testing.T, agentNum int, opts ...tailnettest.DERPAndStunOption) ([]agentWithID, *coderd.ServerTailnet) {
	logger := slogtest.Make(t, nil).Leveled(slog.LevelDebug)
	derpMap, derpServer := tailnettest.RunDERPAndSTUN(t, opts...)

	coord := tailnet.NewCoordinator(logger)
	t.Cleanup(func() {
		_ = coord.Close()
	})

	agents := []agentWithID{}

	for i := 0; i < agentNum; i++ {
		manifest := agentsdk.Manifest{
			AgentID: uuid.New(),
			DERPMap: derpMap,
		}

		c := agenttest.NewClient(t, logger, manifest.AgentID, manifest, make(chan *proto.Stats, 50), coord)
		t.Cleanup(c.Close)

		options := agent.Options{
			Client:     c,
			Filesystem: afero.NewMemMapFs(),
			Logger:     logger.Named("agent"),
		}

		ag := agent.New(options)
		t.Cleanup(func() {
			_ = ag.Close()
		})

		// Wait for the agent to connect.
		require.Eventually(t, func() bool {
			return coord.Node(manifest.AgentID) != nil
		}, testutil.WaitShort, testutil.IntervalFast)

		agents = append(agents, agentWithID{id: manifest.AgentID, Agent: ag})
	}

	serverTailnet, err := coderd.NewServerTailnet(
		context.Background(),
		logger,
		derpServer,
		func() *tailcfg.DERPMap { return derpMap },
		false,
		func(context.Context) (tailnet.MultiAgentConn, error) { return coord.ServeMultiAgent(uuid.New()), nil },
		!derpMap.HasSTUN(),
		trace.NewNoopTracerProvider(),
	)
	require.NoError(t, err)

	t.Cleanup(func() {
		_ = serverTailnet.Close()
	})

	return agents, serverTailnet
}