diff --git a/test/run.go b/test/run.go
new file mode 100644
index 0000000000..67ff413717
--- /dev/null
+++ b/test/run.go
@@ -0,0 +1,454 @@
+// #ignore
+
+// Copyright 2012 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Run runs tests in the test directory.
+// 
+// TODO(bradfitz): docs of some sort, once we figure out how we're changing
+// headers of files
+package main
+
+import (
+	"bytes"
+	"errors"
+	"flag"
+	"fmt"
+	"go/build"
+	"io/ioutil"
+	"log"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"regexp"
+	"runtime"
+	"sort"
+	"strconv"
+	"strings"
+)
+
+var (
+	verbose     = flag.Bool("v", false, "verbose. if set, parallelism is set to 1.")
+	numParallel = flag.Int("n", 8, "number of parallel tests to run")
+	summary     = flag.Bool("summary", false, "show summary of results")
+)
+
+var (
+	// gc and ld are [568][gl].
+	gc, ld string
+
+	// letter is the build.ArchChar
+	letter string
+
+	// dirs are the directories to look for *.go files in.
+	// TODO(bradfitz): just use all directories?
+	dirs = []string{".", "ken", "chan", "interface", "syntax", "dwarf", "fixedbugs", "bugs"}
+
+	// ratec controls the max number of tests running at a time.
+	ratec chan bool
+
+	// toRun is the channel of tests to run.
+	// It is nil until the first test is started.
+	toRun chan *test
+)
+
+// maxTests is an upper bound on the total number of tests.
+// It is used as a channel buffer size to make sure sends don't block.
+const maxTests = 5000
+
+func main() {
+	flag.Parse()
+	if *verbose {
+		*numParallel = 1
+	}
+
+	ratec = make(chan bool, *numParallel)
+	var err error
+	letter, err = build.ArchChar(build.DefaultContext.GOARCH)
+	check(err)
+	gc = letter + "g"
+	ld = letter + "l"
+
+	var tests []*test
+	if flag.NArg() > 0 {
+		for _, arg := range flag.Args() {
+			if arg == "-" || arg == "--" {
+				// Permit running either:
+				// $ go run run.go - env.go
+				// $ go run run.go -- env.go
+				continue
+			}
+			if !strings.HasSuffix(arg, ".go") {
+				log.Fatalf("can't yet deal with non-go file %q", arg)
+			}
+			dir, file := filepath.Split(arg)
+			tests = append(tests, startTest(dir, file))
+		}
+	} else {
+		for _, dir := range dirs {
+			for _, baseGoFile := range goFiles(dir) {
+				tests = append(tests, startTest(dir, baseGoFile))
+			}
+		}
+	}
+
+	failed := false
+	resCount := map[string]int{}
+	for _, test := range tests {
+		<-test.donec
+		_, isSkip := test.err.(skipError)
+		if isSkip {
+			resCount["skip"]++
+			if !*verbose {
+				continue
+			}
+		}
+		errStr := "pass"
+		if test.err != nil {
+			errStr = test.err.Error()
+			if !isSkip {
+				failed = true
+			}
+		}
+		resCount[errStr]++
+		if !*verbose && test.err == nil {
+			continue
+	}
+		fmt.Printf("%-10s %-20s: %s\n", test.action, test.goFileName(), errStr)
+	}
+
+	if *summary {
+		for k, v := range resCount {
+			fmt.Printf("%5d %s\n", v, k)
+		}
+	}
+
+	if failed {
+		os.Exit(1)
+	}
+}
+
+func toolPath(name string) string {
+	p := filepath.Join(os.Getenv("GOROOT"), "bin", "tool", name)
+	if _, err := os.Stat(p); err != nil {
+		log.Fatalf("didn't find binary at %s", p)
+	}
+	return p
+}
+
+func goFiles(dir string) []string {
+	f, err := os.Open(dir)
+	check(err)
+	dirnames, err := f.Readdirnames(-1)
+	check(err)
+	names := []string{}
+	for _, name := range dirnames {
+		if strings.HasSuffix(name, ".go") {
+			names = append(names, name)
+		}
+	}
+	sort.Strings(names)
+	return names
+}
+
+// skipError describes why a test was skipped.
+type skipError string
+
+func (s skipError) Error() string { return string(s) }
+
+func check(err error) {
+	if err != nil {
+		log.Fatal(err)
+	}
+}
+
+// test holds the state of a test.
+type test struct {
+	dir, gofile string
+	donec       chan bool // closed when done
+
+	src    string
+	action string // "compile", "build", "run", "errorcheck"
+
+	tempDir string
+	err     error
+}
+
+// startTest 
+func startTest(dir, gofile string) *test {
+	t := &test{
+		dir:    dir,
+		gofile: gofile,
+		donec:  make(chan bool, 1),
+	}
+	if toRun == nil {
+		toRun = make(chan *test, maxTests)
+		go runTests()
+	}
+	select {
+	case toRun <- t:
+	default:
+		panic("toRun buffer size (maxTests) is too small")
+	}
+	return t
+}
+
+// runTests runs tests in parallel, but respecting the order they
+// were enqueued on the toRun channel.
+func runTests() {
+	for {
+		ratec <- true
+		t := <-toRun
+		go func() {
+			t.run()
+			<-ratec
+		}()
+	}
+}
+
+func (t *test) goFileName() string {
+	return filepath.Join(t.dir, t.gofile)
+}
+
+// run runs a test.
+func (t *test) run() {
+	defer close(t.donec)
+
+	srcBytes, err := ioutil.ReadFile(t.goFileName())
+	if err != nil {
+		t.err = err
+		return
+	}
+	t.src = string(srcBytes)
+	if t.src[0] == '\n' {
+		t.err = skipError("starts with newline")
+		return
+	}
+	pos := strings.Index(t.src, "\n\n")
+	if pos == -1 {
+		t.err = errors.New("double newline not found")
+		return
+	}
+	action := t.src[:pos]
+	if strings.HasPrefix(action, "//") {
+		action = action[2:]
+	}
+	action = strings.TrimSpace(action)
+
+	switch action {
+	case "compile", "build", "run", "errorcheck":
+		t.action = action
+	default:
+		t.err = skipError("skipped; unknown pattern: " + action)
+		t.action = "??"
+		return
+	}
+
+	t.makeTempDir()
+	defer os.RemoveAll(t.tempDir)
+
+	err = ioutil.WriteFile(filepath.Join(t.tempDir, t.gofile), srcBytes, 0644)
+	check(err)
+
+	cmd := exec.Command("go", "tool", gc, "-e", "-o", "a."+letter, t.gofile)
+	var buf bytes.Buffer
+	cmd.Stdout = &buf
+	cmd.Stderr = &buf
+	cmd.Dir = t.tempDir
+	err = cmd.Run()
+	out := buf.String()
+
+	if action == "errorcheck" {
+		t.err = t.errorCheck(out)
+		return
+	}
+
+	if err != nil {
+		t.err = fmt.Errorf("build = %v (%q)", err, out)
+		return
+	}
+
+	if action == "compile" {
+		return
+	}
+
+	if action == "build" || action == "run" {
+		buf.Reset()
+		cmd = exec.Command("go", "tool", ld, "-o", "a.out", "a."+letter)
+		cmd.Stdout = &buf
+		cmd.Stderr = &buf
+		cmd.Dir = t.tempDir
+		err = cmd.Run()
+		out = buf.String()
+		if err != nil {
+			t.err = fmt.Errorf("link = %v (%q)", err, out)
+			return
+		}
+		if action == "build" {
+			return
+		}
+	}
+
+	if action == "run" {
+		buf.Reset()
+		cmd = exec.Command(filepath.Join(t.tempDir, "a.out"))
+		cmd.Stdout = &buf
+		cmd.Stderr = &buf
+		cmd.Dir = t.tempDir
+		cmd.Env = append(cmd.Env, "GOARCH="+runtime.GOARCH)
+		err = cmd.Run()
+		out = buf.String()
+		if err != nil {
+			t.err = fmt.Errorf("run = %v (%q)", err, out)
+			return
+		}
+
+		if out != t.expectedOutput() {
+			t.err = fmt.Errorf("output differs; got:\n%s", out)
+		}
+		return
+	}
+
+	t.err = fmt.Errorf("unimplemented action %q", action)
+}
+
+func (t *test) String() string {
+	return filepath.Join(t.dir, t.gofile)
+}
+
+func (t *test) makeTempDir() {
+	var err error
+	t.tempDir, err = ioutil.TempDir("", "")
+	check(err)
+}
+
+func (t *test) expectedOutput() string {
+	filename := filepath.Join(t.dir, t.gofile)
+	filename = filename[:len(filename)-len(".go")]
+	filename += ".out"
+	b, _ := ioutil.ReadFile(filename)
+	return string(b)
+}
+
+func (t *test) errorCheck(outStr string) (err error) {
+	defer func() {
+		if *verbose && err != nil {
+			log.Printf("%s gc output:\n%s", t, outStr)
+		}
+	}()
+	var errs []error
+
+	var out []string
+	// 6g error messages continue onto additional lines with leading tabs.
+	// Split the output at the beginning of each line that doesn't begin with a tab.
+	for _, line := range strings.Split(outStr, "\n") {
+		if strings.HasPrefix(line, "\t") {
+			out[len(out)-1] += "\n" + line
+		} else {
+			out = append(out, line)
+		}
+	}
+
+	for _, we := range t.wantedErrors() {
+		var errmsgs []string
+		errmsgs, out = partitionStrings(we.filterRe, out)
+		if len(errmsgs) == 0 {
+			errs = append(errs, fmt.Errorf("errchk: %s:%d: missing expected error: %s", we.file, we.lineNum, we.reStr))
+			continue
+		}
+		matched := false
+		for _, errmsg := range errmsgs {
+			if we.re.MatchString(errmsg) {
+				matched = true
+			} else {
+				out = append(out, errmsg)
+			}
+		}
+		if !matched {
+			errs = append(errs, fmt.Errorf("errchk: %s:%d: error(s) on line didn't match pattern: %s", we.file, we.lineNum, we.reStr))
+			continue
+		}
+	}
+
+	if len(errs) == 0 {
+		return nil
+	}
+	if len(errs) == 1 {
+		return errs[0]
+	}
+	var buf bytes.Buffer
+	buf.WriteString("Multiple errors:\n")
+	for _, err := range errs {
+		fmt.Fprintf(&buf, "%s\n", err.Error())
+	}
+	return errors.New(buf.String())
+
+}
+
+func partitionStrings(rx *regexp.Regexp, strs []string) (matched, unmatched []string) {
+	for _, s := range strs {
+		if rx.MatchString(s) {
+			matched = append(matched, s)
+		} else {
+			unmatched = append(unmatched, s)
+		}
+	}
+	return
+}
+
+type wantedError struct {
+	reStr    string
+	re       *regexp.Regexp
+	lineNum  int
+	file     string
+	filterRe *regexp.Regexp // /^file:linenum\b/m
+}
+
+var (
+	errRx       = regexp.MustCompile(`// (?:GC_)?ERROR (.*)`)
+	errQuotesRx = regexp.MustCompile(`"([^"]*)"`)
+	lineRx      = regexp.MustCompile(`LINE(([+-])([0-9]+))?`)
+)
+
+func (t *test) wantedErrors() (errs []wantedError) {
+	for i, line := range strings.Split(t.src, "\n") {
+		lineNum := i + 1
+		if strings.Contains(line, "////") {
+			// double comment disables ERROR
+			continue
+		}
+		m := errRx.FindStringSubmatch(line)
+		if m == nil {
+			continue
+		}
+		all := m[1]
+		mm := errQuotesRx.FindAllStringSubmatch(all, -1)
+		if mm == nil {
+			log.Fatalf("invalid errchk line in %s: %s", t.goFileName(), line)
+		}
+		for _, m := range mm {
+			rx := lineRx.ReplaceAllStringFunc(m[1], func(m string) string {
+				n := lineNum
+				if strings.HasPrefix(m, "LINE+") {
+					delta, _ := strconv.Atoi(m[5:])
+					n += delta
+				} else if strings.HasPrefix(m, "LINE-") {
+					delta, _ := strconv.Atoi(m[5:])
+					n -= delta
+				}
+				return fmt.Sprintf("%s:%d", t.gofile, n)
+			})
+			filterPattern := fmt.Sprintf(`^(\w+/)?%s:%d[:[]`, t.gofile, lineNum)
+			errs = append(errs, wantedError{
+				reStr:    rx,
+				re:       regexp.MustCompile(rx),
+				filterRe: regexp.MustCompile(filterPattern),
+				lineNum:  lineNum,
+				file:     t.gofile,
+			})
+		}
+	}
+
+	return
+}