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: bench_test.go
    path of file: ./repos/garble
    
    the code of the file until where you have to start completion: // Copyright (c) 2020, The Garble Authors.
// See LICENSE for licensing information.

package main

import (
	_ "embed"
	"flag"
	"fmt"
	"os"
	"os/exec"
	"path/filepath"
	"regexp"
	"strconv"
	"strings"
	"testing"
	"time"

	"github.com/go-quicktest/qt"
)

//go:embed testdata/bench/main.go
var benchSourceMain []byte

var (
	rxBuiltRuntime = regexp.MustCompile(`(?m)^runtime$`)
	rxBuiltMain    = regexp.MustCompile(`(?m)^test/main$`)
)

// BenchmarkBuild is a benchmark for 'garble build' on a fairly simple
// main package with a handful of standard library depedencies.
//
// We use a real garble binary and exec it, to simulate what the real user would
// run. The real obfuscation and compilation will happen in sub-processes
// anyway, so skipping one exec layer doesn't help us in any way.
//
// The benchmark isn't parallel, because in practice users build once at a time,
// and each build already spawns concurrent processes and goroutines to do work.
//
// At the moment, each iteration takes 1-2s on a laptop, so we can't make the
// benchmark include any more features unless we make it significantly faster.
func BenchmarkBuild(b *testing.B) {
	// As of Go 1.17, using -benchtime=Nx with N larger than 1 results in two
	// calls to BenchmarkBuild, with the first having b.N==1 to discover
	// sub-benchmarks. Unfortunately, we do a significant amount of work both
	// during setup and during that first iteration, which is pointless.
	// To avoid that, detect the scenario in a hacky way, and return early.
	// See https://github.com/golang/go/issues/32051.
	benchtime := flag.Lookup("test.benchtime").Value.String()
	if b.N == 1 && strings.HasSuffix(benchtime, "x") && benchtime != "1x" {
		return
	}
	tdir := b.TempDir()

	// We collect extra metrics.
	var memoryAllocs, cachedTime, systemTime int64

	outputBin := filepath.Join(tdir, "output")
	sourceDir := filepath.Join(tdir, "src")
	qt.Assert(b, qt.IsNil(os.Mkdir(sourceDir, 0o777)))

	writeSourceFile := func(name string, content []byte) {
		err := os.WriteFile(filepath.Join(sourceDir, name), content, 0o666)
		qt.Assert(b, qt.IsNil(err))
	}
	writeSourceFile("go.mod", []byte("module test/main"))
	writeSourceFile("main.go", benchSourceMain)

	rxGarbleAllocs := regexp.MustCompile(`(?m)^garble allocs: ([0-9]+)`)

	b.ResetTimer()
	b.StopTimer()
	for i := range b.N {
		// First we do a fresh build, using empty cache directories,
		// and the second does an incremental rebuild reusing the same cache directories.
		goCache := filepath.Join(tdir, "go-cache")
		qt.Assert(b, qt.IsNil(os.RemoveAll(goCache)))
		qt.Assert(b, qt.IsNil(os.Mkdir(goCache, 0o777)))
		garbleCache := filepath.Join(tdir, "garble-cache")
		qt.Assert(b, qt.IsNil(os.RemoveAll(garbleCache)))
		qt.Assert(b, qt.IsNil(os.Mkdir(garbleCache, 0o777)))
		env := []string{
			"RUN_GARBLE_MAIN=true",
			"GOCACHE=" + goCache,
			"GARBLE_CACHE=" + garbleCache,
			"GARBLE_WRITE_ALLOCS=true",
		}
		args := []string{"build", "-v", "-o=" + outputBin, sourceDir}

		for _, cached := range []bool{false, true} {
			// The cached rebuil
    
func BenchmarkBuild(b *testing.B) {
	// As of Go 1.17, using -benchtime=Nx with N larger than 1 results in two
	// calls to BenchmarkBuild, with the first having b.N==1 to discover
	// sub-benchmarks. Unfortunately, we do a significant amount of work both
	// during setup and during that first iteration, which is pointless.
	// To avoid that, detect the scenario in a hacky way, and return early.
	// See https://github.com/golang/go/issues/32051.
	benchtime := flag.Lookup("test.benchtime").Value.String()
	if b.N == 1 && strings.HasSuffix(benchtime, "x") && benchtime != "1x" {
		return
	}
	tdir := b.TempDir()

	// We collect extra metrics.
	var memoryAllocs, cachedTime, systemTime int64

	outputBin := filepath.Join(tdir, "output")
	sourceDir := filepath.Join(tdir, "src")
	qt.Assert(b, qt.IsNil(os.Mkdir(sourceDir, 0o777)))

	writeSourceFile := func(name string, content []byte) {
		err := os.WriteFile(filepath.Join(sourceDir, name), content, 0o666)
		qt.Assert(b, qt.IsNil(err))
	}
	writeSourceFile("go.mod", []byte("module test/main"))
	writeSourceFile("main.go", benchSourceMain)

	rxGarbleAllocs := regexp.MustCompile(`(?m)^garble allocs: ([0-9]+)`)

	b.ResetTimer()
	b.StopTimer()
	for i := range b.N {
		// First we do a fresh build, using empty cache directories,
		// and the second does an incremental rebuild reusing the same cache directories.
		goCache := filepath.Join(tdir, "go-cache")
		qt.Assert(b, qt.IsNil(os.RemoveAll(goCache)))
		qt.Assert(b, qt.IsNil(os.Mkdir(goCache, 0o777)))
		garbleCache := filepath.Join(tdir, "garble-cache")
		qt.Assert(b, qt.IsNil(os.RemoveAll(garbleCache)))
		qt.Assert(b, qt.IsNil(os.Mkdir(garbleCache, 0o777)))
		env := []string{
			"RUN_GARBLE_MAIN=true",
			"GOCACHE=" + goCache,
			"GARBLE_CACHE=" + garbleCache,
			"GARBLE_WRITE_ALLOCS=true",
		}
		args := []string{"build", "-v", "-o=" + outputBin, sourceDir}

		for _, cached := range []bool{false, true} {
			// The cached rebuild will reuse all dependencies,
			// but rebuild the main package itself.
			if cached {
				writeSourceFile("rebuild.go", []byte(fmt.Sprintf("package main\nvar v%d int", i)))
			}

			cmd := exec.Command(os.Args[0], args...)
			cmd.Env = append(cmd.Environ(), env...)
			cmd.Dir = sourceDir

			cachedStart := time.Now()
			b.StartTimer()
			out, err := cmd.CombinedOutput()
			b.StopTimer()
			if cached {
				cachedTime += time.Since(cachedStart).Nanoseconds()
			}

			qt.Assert(b, qt.IsNil(err), qt.Commentf("output: %s", out))
			if !cached {
				// Ensure that we built all packages, as expected.
				qt.Assert(b, qt.IsTrue(rxBuiltRuntime.Match(out)))
			} else {
				// Ensure that we only rebuilt the main package, as expected.
				qt.Assert(b, qt.IsFalse(rxBuiltRuntime.Match(out)))
			}
			qt.Assert(b, qt.IsTrue(rxBuiltMain.Match(out)))

			matches := rxGarbleAllocs.FindAllSubmatch(out, -1)
			if !cached {
				// The non-cached version should have at least a handful of
				// sub-processes; catch if our logic breaks.
				qt.Assert(b, qt.IsTrue(len(matches) > 5))
			}
			for _, match := range matches {
				allocs, err := strconv.ParseInt(string(match[1]), 10, 64)
				qt.Assert(b, qt.IsNil(err))
				memoryAllocs += allocs
			}

			systemTime += int64(cmd.ProcessState.SystemTime())
		}
	}
	// We can't use "allocs/op" as it's reserved for ReportAllocs.
	b.ReportMetric(float64(memoryAllocs)/float64(b.N), "mallocs/op")
	b.ReportMetric(float64(cachedTime)/float64(b.N), "cached-ns/op")
	b.ReportMetric(float64(systemTime)/float64(b.N), "sys-ns/op")
	info, err := os.Stat(outputBin)
	if err != nil {
		b.Fatal(err)
	}
	b.ReportMetric(float64(info.Size()), "bin-B")
}