src/pkg/testing/testing.go - go - Git at Google

 // Copyright 2009 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.

 // Package testing provides support for automated testing of Go packages.
 // It is intended to be used in concert with the ``go test'' command, which automates
 // execution of any function of the form
 //     func TestXxx(*testing.T)
 // where Xxx can be any alphanumeric string (but the first letter must not be in
 // [a-z]) and serves to identify the test routine.
 //
 // Within these functions, use the Error, Fail or related methods to signal failure.
 //
 // To write a new test suite, create a file whose name ends _test.go that
 // contains the TestXxx functions as described here. Put the file in the same
 // package as the one being tested. The file will be excluded from regular
 // package builds but will be included when the ``go test'' command is run.
 // For more detail, run ``go help test'' and ``go help testflag''.
 //
 // Tests and benchmarks may be skipped if not applicable with a call to
 // the Skip method of *T and *B:
 //     func TestTimeConsuming(t *testing.T) {
 //         if testing.Short() {
 //             t.Skip("skipping test in short mode.")
 //         }
 //         ...
 //     }
 //
 // Benchmarks
 //
 // Functions of the form
 //     func BenchmarkXxx(*testing.B)
 // are considered benchmarks, and are executed by the "go test" command when
 // its -bench flag is provided. Benchmarks are run sequentially.
 //
 // For a description of the testing flags, see
 // http://golang.org/cmd/go/#hdr-Description_of_testing_flags.
 //
 // A sample benchmark function looks like this:
 //     func BenchmarkHello(b *testing.B) {
 //         for i := 0; i < b.N; i++ {
 //             fmt.Sprintf("hello")
 //         }
 //     }
 //
 // The benchmark function must run the target code b.N times.
 // The benchmark package will vary b.N until the benchmark function lasts
 // long enough to be timed reliably.  The output
 //     BenchmarkHello    10000000    282 ns/op
 // means that the loop ran 10000000 times at a speed of 282 ns per loop.
 //
 // If a benchmark needs some expensive setup before running, the timer
 // may be reset:
 //
 //     func BenchmarkBigLen(b *testing.B) {
 //         big := NewBig()
 //         b.ResetTimer()
 //         for i := 0; i < b.N; i++ {
 //             big.Len()
 //         }
 //     }
 //
 // If a benchmark needs to test performance in a parallel setting, it may use
 // the RunParallel helper function; such benchmarks are intended to be used with
 // the go test -cpu flag:
 //
 //     func BenchmarkTemplateParallel(b *testing.B) {
 //         templ := template.Must(template.New("test").Parse("Hello, {{.}}!"))
 //         b.RunParallel(func(pb *testing.PB) {
 //             var buf bytes.Buffer
 //             for pb.Next() {
 //                 buf.Reset()
 //                 templ.Execute(&buf, "World")
 //             }
 //         })
 //     }
 //
 // Examples
 //
 // The package also runs and verifies example code. Example functions may
 // include a concluding line comment that begins with "Output:" and is compared with
 // the standard output of the function when the tests are run. (The comparison
 // ignores leading and trailing space.) These are examples of an example:
 //
 //     func ExampleHello() {
 //             fmt.Println("hello")
 //             // Output: hello
 //     }
 //
 //     func ExampleSalutations() {
 //             fmt.Println("hello, and")
 //             fmt.Println("goodbye")
 //             // Output:
 //             // hello, and
 //             // goodbye
 //     }
 //
 // Example functions without output comments are compiled but not executed.
 //
 // The naming convention to declare examples for the package, a function F, a type T and
 // method M on type T are:
 //
 //     func Example() { ... }
 //     func ExampleF() { ... }
 //     func ExampleT() { ... }
 //     func ExampleT_M() { ... }
 //
 // Multiple example functions for a package/type/function/method may be provided by
 // appending a distinct suffix to the name. The suffix must start with a
 // lower-case letter.
 //
 //     func Example_suffix() { ... }
 //     func ExampleF_suffix() { ... }
 //     func ExampleT_suffix() { ... }
 //     func ExampleT_M_suffix() { ... }
 //
 // The entire test file is presented as the example when it contains a single
 // example function, at least one other function, type, variable, or constant
 // declaration, and no test or benchmark functions.
 package testing

 import (
 	"bytes"
 	"flag"
 	"fmt"
 	"os"
 	"runtime"
 	"runtime/pprof"
 	"strconv"
 	"strings"
 	"sync"
 	"time"
 )

 var (
 	// The short flag requests that tests run more quickly, but its functionality
 	// is provided by test writers themselves.  The testing package is just its
 	// home.  The all.bash installation script sets it to make installation more
 	// efficient, but by default the flag is off so a plain "go test" will do a
 	// full test of the package.
 	short = flag.Bool("test.short", false, "run smaller test suite to save time")

 	// The directory in which to create profile files and the like. When run from
 	// "go test", the binary always runs in the source directory for the package;
 	// this flag lets "go test" tell the binary to write the files in the directory where
 	// the "go test" command is run.
 	outputDir = flag.String("test.outputdir", "", "directory in which to write profiles")

 	// Report as tests are run; default is silent for success.
 	chatty           = flag.Bool("test.v", false, "verbose: print additional output")
 	coverProfile     = flag.String("test.coverprofile", "", "write a coverage profile to the named file after execution")
 	match            = flag.String("test.run", "", "regular expression to select tests and examples to run")
 	memProfile       = flag.String("test.memprofile", "", "write a memory profile to the named file after execution")
 	memProfileRate   = flag.Int("test.memprofilerate", 0, "if >=0, sets runtime.MemProfileRate")
 	cpuProfile       = flag.String("test.cpuprofile", "", "write a cpu profile to the named file during execution")
 	blockProfile     = flag.String("test.blockprofile", "", "write a goroutine blocking profile to the named file after execution")
 	blockProfileRate = flag.Int("test.blockprofilerate", 1, "if >= 0, calls runtime.SetBlockProfileRate()")
 	timeout          = flag.Duration("test.timeout", 0, "if positive, sets an aggregate time limit for all tests")
 	cpuListStr       = flag.String("test.cpu", "", "comma-separated list of number of CPUs to use for each test")
 	parallel         = flag.Int("test.parallel", runtime.GOMAXPROCS(0), "maximum test parallelism")

 	haveExamples bool // are there examples?

 	cpuList []int
 )

 // common holds the elements common between T and B and
 // captures common methods such as Errorf.
 type common struct {
 	mu       sync.RWMutex // guards output and failed
 	output   []byte       // Output generated by test or benchmark.
 	failed   bool         // Test or benchmark has failed.
 	skipped  bool         // Test of benchmark has been skipped.
 	finished bool

 	start    time.Time // Time test or benchmark started
 	duration time.Duration
 	self     interface{}      // To be sent on signal channel when done.
 	signal   chan interface{} // Output for serial tests.
 }

 // Short reports whether the -test.short flag is set.
 func Short() bool {
 	return *short
 }

 // Verbose reports whether the -test.v flag is set.
 func Verbose() bool {
 	return *chatty
 }

 // decorate prefixes the string with the file and line of the call site
 // and inserts the final newline if needed and indentation tabs for formatting.
 func decorate(s string) string {
 	_, file, line, ok := runtime.Caller(3) // decorate + log + public function.
 	if ok {
 		// Truncate file name at last file name separator.
 		if index := strings.LastIndex(file, "/"); index >= 0 {
 			file = file[index+1:]
 		} else if index = strings.LastIndex(file, "\\"); index >= 0 {
 			file = file[index+1:]
 		}
 	} else {
 		file = "???"
 		line = 1
 	}
 	buf := new(bytes.Buffer)
 	// Every line is indented at least one tab.
 	buf.WriteByte('\t')
 	fmt.Fprintf(buf, "%s:%d: ", file, line)
 	lines := strings.Split(s, "\n")
 	if l := len(lines); l > 1 && lines[l-1] == "" {
 		lines = lines[:l-1]
 	}
 	for i, line := range lines {
 		if i > 0 {
 			// Second and subsequent lines are indented an extra tab.
 			buf.WriteString("\n\t\t")
 		}
 		buf.WriteString(line)
 	}
 	buf.WriteByte('\n')
 	return buf.String()
 }

 // TB is the interface common to T and B.
 type TB interface {
 	Error(args ...interface{})
 	Errorf(format string, args ...interface{})
 	Fail()
 	FailNow()
 	Failed() bool
 	Fatal(args ...interface{})
 	Fatalf(format string, args ...interface{})
 	Log(args ...interface{})
 	Logf(format string, args ...interface{})
 	Skip(args ...interface{})
 	SkipNow()
 	Skipf(format string, args ...interface{})
 	Skipped() bool

 	// A private method to prevent users implementing the
 	// interface and so future additions to it will not
 	// violate Go 1 compatibility.
 	private()
 }

 var _ TB = (*T)(nil)
 var _ TB = (*B)(nil)

 // T is a type passed to Test functions to manage test state and support formatted test logs.
 // Logs are accumulated during execution and dumped to standard error when done.
 type T struct {
 	common
 	name          string    // Name of test.
 	startParallel chan bool // Parallel tests will wait on this.
 }

 func (c *common) private() {}

 // Fail marks the function as having failed but continues execution.
 func (c *common) Fail() {
 	c.mu.Lock()
 	defer c.mu.Unlock()
 	c.failed = true
 }

 // Failed reports whether the function has failed.
 func (c *common) Failed() bool {
 	c.mu.RLock()
 	defer c.mu.RUnlock()
 	return c.failed
 }

 // FailNow marks the function as having failed and stops its execution.
 // Execution will continue at the next test or benchmark.
 // FailNow must be called from the goroutine running the
 // test or benchmark function, not from other goroutines
 // created during the test. Calling FailNow does not stop
 // those other goroutines.
 func (c *common) FailNow() {
 	c.Fail()

 	// Calling runtime.Goexit will exit the goroutine, which
 	// will run the deferred functions in this goroutine,
 	// which will eventually run the deferred lines in tRunner,
 	// which will signal to the test loop that this test is done.
 	//
 	// A previous version of this code said:
 	//
 	//	c.duration = ...
 	//	c.signal <- c.self
 	//	runtime.Goexit()
 	//
 	// This previous version duplicated code (those lines are in
 	// tRunner no matter what), but worse the goroutine teardown
 	// implicit in runtime.Goexit was not guaranteed to complete
 	// before the test exited.  If a test deferred an important cleanup
 	// function (like removing temporary files), there was no guarantee
 	// it would run on a test failure.  Because we send on c.signal during
 	// a top-of-stack deferred function now, we know that the send
 	// only happens after any other stacked defers have completed.
 	c.finished = true
 	runtime.Goexit()
 }

 // log generates the output. It's always at the same stack depth.
 func (c *common) log(s string) {
 	c.mu.Lock()
 	defer c.mu.Unlock()
 	c.output = append(c.output, decorate(s)...)
 }

 // Log formats its arguments using default formatting, analogous to Println,
 // and records the text in the error log. The text will be printed only if
 // the test fails or the -test.v flag is set.
 func (c *common) Log(args ...interface{}) { c.log(fmt.Sprintln(args...)) }

 // Logf formats its arguments according to the format, analogous to Printf,
 // and records the text in the error log. The text will be printed only if
 // the test fails or the -test.v flag is set.
 func (c *common) Logf(format string, args ...interface{}) { c.log(fmt.Sprintf(format, args...)) }

 // Error is equivalent to Log followed by Fail.
 func (c *common) Error(args ...interface{}) {
 	c.log(fmt.Sprintln(args...))
 	c.Fail()
 }

 // Errorf is equivalent to Logf followed by Fail.
 func (c *common) Errorf(format string, args ...interface{}) {
 	c.log(fmt.Sprintf(format, args...))
 	c.Fail()
 }

 // Fatal is equivalent to Log followed by FailNow.
 func (c *common) Fatal(args ...interface{}) {
 	c.log(fmt.Sprintln(args...))
 	c.FailNow()
 }

 // Fatalf is equivalent to Logf followed by FailNow.
 func (c *common) Fatalf(format string, args ...interface{}) {
 	c.log(fmt.Sprintf(format, args...))
 	c.FailNow()
 }

 // Skip is equivalent to Log followed by SkipNow.
 func (c *common) Skip(args ...interface{}) {
 	c.log(fmt.Sprintln(args...))
 	c.SkipNow()
 }

 // Skipf is equivalent to Logf followed by SkipNow.
 func (c *common) Skipf(format string, args ...interface{}) {
 	c.log(fmt.Sprintf(format, args...))
 	c.SkipNow()
 }

 // SkipNow marks the test as having been skipped and stops its execution.
 // Execution will continue at the next test or benchmark. See also FailNow.
 // SkipNow must be called from the goroutine running the test, not from
 // other goroutines created during the test. Calling SkipNow does not stop
 // those other goroutines.
 func (c *common) SkipNow() {
 	c.skip()
 	c.finished = true
 	runtime.Goexit()
 }

 func (c *common) skip() {
 	c.mu.Lock()
 	defer c.mu.Unlock()
 	c.skipped = true
 }

 // Skipped reports whether the test was skipped.
 func (c *common) Skipped() bool {
 	c.mu.RLock()
 	defer c.mu.RUnlock()
 	return c.skipped
 }

 // Parallel signals that this test is to be run in parallel with (and only with)
 // other parallel tests.
 func (t *T) Parallel() {
 	t.signal <- (*T)(nil) // Release main testing loop
 	<-t.startParallel     // Wait for serial tests to finish
 	// Assuming Parallel is the first thing a test does, which is reasonable,
 	// reinitialize the test's start time because it's actually starting now.
 	t.start = time.Now()
 }

 // An internal type but exported because it is cross-package; part of the implementation
 // of the "go test" command.
 type InternalTest struct {
 	Name string
 	F    func(*T)
 }

 func tRunner(t *T, test *InternalTest) {
 	// When this goroutine is done, either because test.F(t)
 	// returned normally or because a test failure triggered
 	// a call to runtime.Goexit, record the duration and send
 	// a signal saying that the test is done.
 	defer func() {
 		t.duration = time.Now().Sub(t.start)
 		// If the test panicked, print any test output before dying.
 		err := recover()
 		if !t.finished && err == nil {
 			err = fmt.Errorf("test executed panic(nil) or runtime.Goexit")
 		}
 		if err != nil {
 			t.Fail()
 			t.report()
 			panic(err)
 		}
 		t.signal <- t
 	}()

 	t.start = time.Now()
 	test.F(t)
 	t.finished = true
 }

 // An internal function but exported because it is cross-package; part of the implementation
 // of the "go test" command.
 func Main(matchString func(pat, str string) (bool, error), tests []InternalTest, benchmarks []InternalBenchmark, examples []InternalExample) {
 	flag.Parse()
 	parseCpuList()

 	before()
 	startAlarm()
 	haveExamples = len(examples) > 0
 	testOk := RunTests(matchString, tests)
 	exampleOk := RunExamples(matchString, examples)
 	stopAlarm()
 	if !testOk || !exampleOk {
 		fmt.Println("FAIL")
 		after()
 		os.Exit(1)
 	}
 	fmt.Println("PASS")
 	RunBenchmarks(matchString, benchmarks)
 	after()
 }

 func (t *T) report() {
 	tstr := fmt.Sprintf("(%.2f seconds)", t.duration.Seconds())
 	format := "--- %s: %s %s\n%s"
 	if t.Failed() {
 		fmt.Printf(format, "FAIL", t.name, tstr, t.output)
 	} else if *chatty {
 		if t.Skipped() {
 			fmt.Printf(format, "SKIP", t.name, tstr, t.output)
 		} else {
 			fmt.Printf(format, "PASS", t.name, tstr, t.output)
 		}
 	}
 }

 func RunTests(matchString func(pat, str string) (bool, error), tests []InternalTest) (ok bool) {
 	ok = true
 	if len(tests) == 0 && !haveExamples {
 		fmt.Fprintln(os.Stderr, "testing: warning: no tests to run")
 		return
 	}
 	for _, procs := range cpuList {
 		runtime.GOMAXPROCS(procs)
 		// We build a new channel tree for each run of the loop.
 		// collector merges in one channel all the upstream signals from parallel tests.
 		// If all tests pump to the same channel, a bug can occur where a test
 		// kicks off a goroutine that Fails, yet the test still delivers a completion signal,
 		// which skews the counting.
 		var collector = make(chan interface{})

 		numParallel := 0
 		startParallel := make(chan bool)

 		for i := 0; i < len(tests); i++ {
 			matched, err := matchString(*match, tests[i].Name)
 			if err != nil {
 				fmt.Fprintf(os.Stderr, "testing: invalid regexp for -test.run: %s\n", err)
 				os.Exit(1)
 			}
 			if !matched {
 				continue
 			}
 			testName := tests[i].Name
 			if procs != 1 {
 				testName = fmt.Sprintf("%s-%d", tests[i].Name, procs)
 			}
 			t := &T{
 				common: common{
 					signal: make(chan interface{}),
 				},
 				name:          testName,
 				startParallel: startParallel,
 			}
 			t.self = t
 			if *chatty {
 				fmt.Printf("=== RUN %s\n", t.name)
 			}
 			go tRunner(t, &tests[i])
 			out := (<-t.signal).(*T)
 			if out == nil { // Parallel run.
 				go func() {
 					collector <- <-t.signal
 				}()
 				numParallel++
 				continue
 			}
 			t.report()
 			ok = ok && !out.Failed()
 		}

 		running := 0
 		for numParallel+running > 0 {
 			if running < *parallel && numParallel > 0 {
 				startParallel <- true
 				running++
 				numParallel--
 				continue
 			}
 			t := (<-collector).(*T)
 			t.report()
 			ok = ok && !t.Failed()
 			running--
 		}
 	}
 	return
 }

 // before runs before all testing.
 func before() {
 	if *memProfileRate > 0 {
 		runtime.MemProfileRate = *memProfileRate
 	}
 	if *cpuProfile != "" {
 		f, err := os.Create(toOutputDir(*cpuProfile))
 		if err != nil {
 			fmt.Fprintf(os.Stderr, "testing: %s", err)
 			return
 		}
 		if err := pprof.StartCPUProfile(f); err != nil {
 			fmt.Fprintf(os.Stderr, "testing: can't start cpu profile: %s", err)
 			f.Close()
 			return
 		}
 		// Could save f so after can call f.Close; not worth the effort.
 	}
 	if *blockProfile != "" && *blockProfileRate >= 0 {
 		runtime.SetBlockProfileRate(*blockProfileRate)
 	}
 	if *coverProfile != "" && cover.Mode == "" {
 		fmt.Fprintf(os.Stderr, "testing: cannot use -test.coverprofile because test binary was not built with coverage enabled\n")
 		os.Exit(2)
 	}
 }

 // after runs after all testing.
 func after() {
 	if *cpuProfile != "" {
 		pprof.StopCPUProfile() // flushes profile to disk
 	}
 	if *memProfile != "" {
 		f, err := os.Create(toOutputDir(*memProfile))
 		if err != nil {
 			fmt.Fprintf(os.Stderr, "testing: %s\n", err)
 			os.Exit(2)
 		}
 		if err = pprof.WriteHeapProfile(f); err != nil {
 			fmt.Fprintf(os.Stderr, "testing: can't write %s: %s\n", *memProfile, err)
 			os.Exit(2)
 		}
 		f.Close()
 	}
 	if *blockProfile != "" && *blockProfileRate >= 0 {
 		f, err := os.Create(toOutputDir(*blockProfile))
 		if err != nil {
 			fmt.Fprintf(os.Stderr, "testing: %s\n", err)
 			os.Exit(2)
 		}
 		if err = pprof.Lookup("block").WriteTo(f, 0); err != nil {
 			fmt.Fprintf(os.Stderr, "testing: can't write %s: %s\n", *blockProfile, err)
 			os.Exit(2)
 		}
 		f.Close()
 	}
 	if cover.Mode != "" {
 		coverReport()
 	}
 }

 // toOutputDir returns the file name relocated, if required, to outputDir.
 // Simple implementation to avoid pulling in path/filepath.
 func toOutputDir(path string) string {
 	if *outputDir == "" || path == "" {
 		return path
 	}
 	if runtime.GOOS == "windows" {
 		// On Windows, it's clumsy, but we can be almost always correct
 		// by just looking for a drive letter and a colon.
 		// Absolute paths always have a drive letter (ignoring UNC).
 		// Problem: if path == "C:A" and outputdir == "C:\Go" it's unclear
 		// what to do, but even then path/filepath doesn't help.
 		// TODO: Worth doing better? Probably not, because we're here only
 		// under the management of go test.
 		if len(path) >= 2 {
 			letter, colon := path[0], path[1]
 			if ('a' <= letter && letter <= 'z' || 'A' <= letter && letter <= 'Z') && colon == ':' {
 				// If path starts with a drive letter we're stuck with it regardless.
 				return path
 			}
 		}
 	}
 	if os.IsPathSeparator(path[0]) {
 		return path
 	}
 	return fmt.Sprintf("%s%c%s", *outputDir, os.PathSeparator, path)
 }

 var timer *time.Timer

 // startAlarm starts an alarm if requested.
 func startAlarm() {
 	if *timeout > 0 {
 		timer = time.AfterFunc(*timeout, func() {
 			panic(fmt.Sprintf("test timed out after %v", *timeout))
 		})
 	}
 }

 // stopAlarm turns off the alarm.
 func stopAlarm() {
 	if *timeout > 0 {
 		timer.Stop()
 	}
 }

 func parseCpuList() {
 	for _, val := range strings.Split(*cpuListStr, ",") {
 		val = strings.TrimSpace(val)
 		if val == "" {
 			continue
 		}
 		cpu, err := strconv.Atoi(val)
 		if err != nil || cpu <= 0 {
 			fmt.Fprintf(os.Stderr, "testing: invalid value %q for -test.cpu\n", val)
 			os.Exit(1)
 		}
 		cpuList = append(cpuList, cpu)
 	}
 	if cpuList == nil {
 		cpuList = append(cpuList, runtime.GOMAXPROCS(-1))
 	}
 }
	// Copyright 2009 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.

	// Package testing provides support for automated testing of Go packages.
	// It is intended to be used in concert with the ``go test'' command, which automates
	// execution of any function of the form
	// func TestXxx(*testing.T)
	// where Xxx can be any alphanumeric string (but the first letter must not be in
	// [a-z]) and serves to identify the test routine.
	//
	// Within these functions, use the Error, Fail or related methods to signal failure.
	//
	// To write a new test suite, create a file whose name ends _test.go that
	// contains the TestXxx functions as described here. Put the file in the same
	// package as the one being tested. The file will be excluded from regular
	// package builds but will be included when the ``go test'' command is run.
	// For more detail, run ``go help test'' and ``go help testflag''.
	//
	// Tests and benchmarks may be skipped if not applicable with a call to
	// the Skip method of T and B:
	// func TestTimeConsuming(t *testing.T) {
	// if testing.Short() {
	// t.Skip("skipping test in short mode.")
	// }
	// ...
	// }
	//
	// Benchmarks
	//
	// Functions of the form
	// func BenchmarkXxx(*testing.B)
	// are considered benchmarks, and are executed by the "go test" command when
	// its -bench flag is provided. Benchmarks are run sequentially.
	//
	// For a description of the testing flags, see
	// http://golang.org/cmd/go/#hdr-Description_of_testing_flags.
	//
	// A sample benchmark function looks like this:
	// func BenchmarkHello(b *testing.B) {
	// for i := 0; i < b.N; i++ {
	// fmt.Sprintf("hello")
	// }
	// }
	//
	// The benchmark function must run the target code b.N times.
	// The benchmark package will vary b.N until the benchmark function lasts
	// long enough to be timed reliably. The output
	// BenchmarkHello 10000000 282 ns/op
	// means that the loop ran 10000000 times at a speed of 282 ns per loop.
	//
	// If a benchmark needs some expensive setup before running, the timer
	// may be reset:
	//
	// func BenchmarkBigLen(b *testing.B) {
	// big := NewBig()
	// b.ResetTimer()
	// for i := 0; i < b.N; i++ {
	// big.Len()
	// }
	// }
	//
	// If a benchmark needs to test performance in a parallel setting, it may use
	// the RunParallel helper function; such benchmarks are intended to be used with
	// the go test -cpu flag:
	//
	// func BenchmarkTemplateParallel(b *testing.B) {
	// templ := template.Must(template.New("test").Parse("Hello, {{.}}!"))
	// b.RunParallel(func(pb *testing.PB) {
	// var buf bytes.Buffer
	// for pb.Next() {
	// buf.Reset()
	// templ.Execute(&buf, "World")
	// }
	// })
	// }
	//
	// Examples
	//
	// The package also runs and verifies example code. Example functions may
	// include a concluding line comment that begins with "Output:" and is compared with
	// the standard output of the function when the tests are run. (The comparison
	// ignores leading and trailing space.) These are examples of an example:
	//
	// func ExampleHello() {
	// fmt.Println("hello")
	// // Output: hello
	// }
	//
	// func ExampleSalutations() {
	// fmt.Println("hello, and")
	// fmt.Println("goodbye")
	// // Output:
	// // hello, and
	// // goodbye
	// }
	//
	// Example functions without output comments are compiled but not executed.
	//
	// The naming convention to declare examples for the package, a function F, a type T and
	// method M on type T are:
	//
	// func Example() { ... }
	// func ExampleF() { ... }
	// func ExampleT() { ... }
	// func ExampleT_M() { ... }
	//
	// Multiple example functions for a package/type/function/method may be provided by
	// appending a distinct suffix to the name. The suffix must start with a
	// lower-case letter.
	//
	// func Example_suffix() { ... }
	// func ExampleF_suffix() { ... }
	// func ExampleT_suffix() { ... }
	// func ExampleT_M_suffix() { ... }
	//
	// The entire test file is presented as the example when it contains a single
	// example function, at least one other function, type, variable, or constant
	// declaration, and no test or benchmark functions.
	package testing

	import (
	"bytes"
	"flag"
	"fmt"
	"os"
	"runtime"
	"runtime/pprof"
	"strconv"
	"strings"
	"sync"
	"time"
	)

	var (
	// The short flag requests that tests run more quickly, but its functionality
	// is provided by test writers themselves. The testing package is just its
	// home. The all.bash installation script sets it to make installation more
	// efficient, but by default the flag is off so a plain "go test" will do a
	// full test of the package.
	short = flag.Bool("test.short", false, "run smaller test suite to save time")

	// The directory in which to create profile files and the like. When run from
	// "go test", the binary always runs in the source directory for the package;
	// this flag lets "go test" tell the binary to write the files in the directory where
	// the "go test" command is run.
	outputDir = flag.String("test.outputdir", "", "directory in which to write profiles")

	// Report as tests are run; default is silent for success.
	chatty = flag.Bool("test.v", false, "verbose: print additional output")
	coverProfile = flag.String("test.coverprofile", "", "write a coverage profile to the named file after execution")
	match = flag.String("test.run", "", "regular expression to select tests and examples to run")
	memProfile = flag.String("test.memprofile", "", "write a memory profile to the named file after execution")
	memProfileRate = flag.Int("test.memprofilerate", 0, "if >=0, sets runtime.MemProfileRate")
	cpuProfile = flag.String("test.cpuprofile", "", "write a cpu profile to the named file during execution")
	blockProfile = flag.String("test.blockprofile", "", "write a goroutine blocking profile to the named file after execution")
	blockProfileRate = flag.Int("test.blockprofilerate", 1, "if >= 0, calls runtime.SetBlockProfileRate()")
	timeout = flag.Duration("test.timeout", 0, "if positive, sets an aggregate time limit for all tests")
	cpuListStr = flag.String("test.cpu", "", "comma-separated list of number of CPUs to use for each test")
	parallel = flag.Int("test.parallel", runtime.GOMAXPROCS(0), "maximum test parallelism")

	haveExamples bool // are there examples?

	cpuList []int
	)

	// common holds the elements common between T and B and
	// captures common methods such as Errorf.
	type common struct {
	mu sync.RWMutex // guards output and failed
	output []byte // Output generated by test or benchmark.
	failed bool // Test or benchmark has failed.
	skipped bool // Test of benchmark has been skipped.
	finished bool

	start time.Time // Time test or benchmark started
	duration time.Duration
	self interface{} // To be sent on signal channel when done.
	signal chan interface{} // Output for serial tests.
	}

	// Short reports whether the -test.short flag is set.
	func Short() bool {
	return *short
	}

	// Verbose reports whether the -test.v flag is set.
	func Verbose() bool {
	return *chatty
	}

	// decorate prefixes the string with the file and line of the call site
	// and inserts the final newline if needed and indentation tabs for formatting.
	func decorate(s string) string {
	_, file, line, ok := runtime.Caller(3) // decorate + log + public function.
	if ok {
	// Truncate file name at last file name separator.
	if index := strings.LastIndex(file, "/"); index >= 0 {
	file = file[index+1:]
	} else if index = strings.LastIndex(file, "\\"); index >= 0 {
	file = file[index+1:]
	}
	} else {
	file = "???"
	line = 1
	}
	buf := new(bytes.Buffer)
	// Every line is indented at least one tab.
	buf.WriteByte('\t')
	fmt.Fprintf(buf, "%s:%d: ", file, line)
	lines := strings.Split(s, "\n")
	if l := len(lines); l > 1 && lines[l-1] == "" {
	lines = lines[:l-1]
	}
	for i, line := range lines {
	if i > 0 {
	// Second and subsequent lines are indented an extra tab.
	buf.WriteString("\n\t\t")
	}
	buf.WriteString(line)
	}
	buf.WriteByte('\n')
	return buf.String()
	}

	// TB is the interface common to T and B.
	type TB interface {
	Error(args ...interface{})
	Errorf(format string, args ...interface{})
	Fail()
	FailNow()
	Failed() bool
	Fatal(args ...interface{})
	Fatalf(format string, args ...interface{})
	Log(args ...interface{})
	Logf(format string, args ...interface{})
	Skip(args ...interface{})
	SkipNow()
	Skipf(format string, args ...interface{})
	Skipped() bool

	// A private method to prevent users implementing the
	// interface and so future additions to it will not
	// violate Go 1 compatibility.
	private()
	}

	var _ TB = (*T)(nil)
	var _ TB = (*B)(nil)

	// T is a type passed to Test functions to manage test state and support formatted test logs.
	// Logs are accumulated during execution and dumped to standard error when done.
	type T struct {
	common
	name string // Name of test.
	startParallel chan bool // Parallel tests will wait on this.
	}

	func (c *common) private() {}

	// Fail marks the function as having failed but continues execution.
	func (c *common) Fail() {
	c.mu.Lock()
	defer c.mu.Unlock()
	c.failed = true
	}

	// Failed reports whether the function has failed.
	func (c *common) Failed() bool {
	c.mu.RLock()
	defer c.mu.RUnlock()
	return c.failed
	}

	// FailNow marks the function as having failed and stops its execution.
	// Execution will continue at the next test or benchmark.
	// FailNow must be called from the goroutine running the
	// test or benchmark function, not from other goroutines
	// created during the test. Calling FailNow does not stop
	// those other goroutines.
	func (c *common) FailNow() {
	c.Fail()

	// Calling runtime.Goexit will exit the goroutine, which
	// will run the deferred functions in this goroutine,
	// which will eventually run the deferred lines in tRunner,
	// which will signal to the test loop that this test is done.
	//
	// A previous version of this code said:
	//
	// c.duration = ...
	// c.signal <- c.self
	// runtime.Goexit()
	//
	// This previous version duplicated code (those lines are in
	// tRunner no matter what), but worse the goroutine teardown
	// implicit in runtime.Goexit was not guaranteed to complete
	// before the test exited. If a test deferred an important cleanup
	// function (like removing temporary files), there was no guarantee
	// it would run on a test failure. Because we send on c.signal during
	// a top-of-stack deferred function now, we know that the send
	// only happens after any other stacked defers have completed.
	c.finished = true
	runtime.Goexit()
	}

	// log generates the output. It's always at the same stack depth.
	func (c *common) log(s string) {
	c.mu.Lock()
	defer c.mu.Unlock()
	c.output = append(c.output, decorate(s)...)
	}

	// Log formats its arguments using default formatting, analogous to Println,
	// and records the text in the error log. The text will be printed only if
	// the test fails or the -test.v flag is set.
	func (c *common) Log(args ...interface{}) { c.log(fmt.Sprintln(args...)) }

	// Logf formats its arguments according to the format, analogous to Printf,
	// and records the text in the error log. The text will be printed only if
	// the test fails or the -test.v flag is set.
	func (c *common) Logf(format string, args ...interface{}) { c.log(fmt.Sprintf(format, args...)) }

	// Error is equivalent to Log followed by Fail.
	func (c *common) Error(args ...interface{}) {
	c.log(fmt.Sprintln(args...))
	c.Fail()
	}

	// Errorf is equivalent to Logf followed by Fail.
	func (c *common) Errorf(format string, args ...interface{}) {
	c.log(fmt.Sprintf(format, args...))
	c.Fail()
	}

	// Fatal is equivalent to Log followed by FailNow.
	func (c *common) Fatal(args ...interface{}) {
	c.log(fmt.Sprintln(args...))
	c.FailNow()
	}

	// Fatalf is equivalent to Logf followed by FailNow.
	func (c *common) Fatalf(format string, args ...interface{}) {
	c.log(fmt.Sprintf(format, args...))
	c.FailNow()
	}

	// Skip is equivalent to Log followed by SkipNow.
	func (c *common) Skip(args ...interface{}) {
	c.log(fmt.Sprintln(args...))
	c.SkipNow()
	}

	// Skipf is equivalent to Logf followed by SkipNow.
	func (c *common) Skipf(format string, args ...interface{}) {
	c.log(fmt.Sprintf(format, args...))
	c.SkipNow()
	}

	// SkipNow marks the test as having been skipped and stops its execution.
	// Execution will continue at the next test or benchmark. See also FailNow.
	// SkipNow must be called from the goroutine running the test, not from
	// other goroutines created during the test. Calling SkipNow does not stop
	// those other goroutines.
	func (c *common) SkipNow() {
	c.skip()
	c.finished = true
	runtime.Goexit()
	}

	func (c *common) skip() {
	c.mu.Lock()
	defer c.mu.Unlock()
	c.skipped = true
	}

	// Skipped reports whether the test was skipped.
	func (c *common) Skipped() bool {
	c.mu.RLock()
	defer c.mu.RUnlock()
	return c.skipped
	}

	// Parallel signals that this test is to be run in parallel with (and only with)
	// other parallel tests.
	func (t *T) Parallel() {
	t.signal <- (*T)(nil) // Release main testing loop
	<-t.startParallel // Wait for serial tests to finish
	// Assuming Parallel is the first thing a test does, which is reasonable,
	// reinitialize the test's start time because it's actually starting now.
	t.start = time.Now()
	}

	// An internal type but exported because it is cross-package; part of the implementation
	// of the "go test" command.
	type InternalTest struct {
	Name string
	F func(*T)
	}

	func tRunner(t T, test InternalTest) {
	// When this goroutine is done, either because test.F(t)
	// returned normally or because a test failure triggered
	// a call to runtime.Goexit, record the duration and send
	// a signal saying that the test is done.
	defer func() {
	t.duration = time.Now().Sub(t.start)
	// If the test panicked, print any test output before dying.
	err := recover()
	if !t.finished && err == nil {
	err = fmt.Errorf("test executed panic(nil) or runtime.Goexit")
	}
	if err != nil {
	t.Fail()
	t.report()
	panic(err)
	}
	t.signal <- t
	}()

	t.start = time.Now()
	test.F(t)
	t.finished = true
	}

	// An internal function but exported because it is cross-package; part of the implementation
	// of the "go test" command.
	func Main(matchString func(pat, str string) (bool, error), tests []InternalTest, benchmarks []InternalBenchmark, examples []InternalExample) {
	flag.Parse()
	parseCpuList()

	before()
	startAlarm()
	haveExamples = len(examples) > 0
	testOk := RunTests(matchString, tests)
	exampleOk := RunExamples(matchString, examples)
	stopAlarm()
	if !testOk \|\| !exampleOk {
	fmt.Println("FAIL")
	after()
	os.Exit(1)
	}
	fmt.Println("PASS")
	RunBenchmarks(matchString, benchmarks)
	after()
	}

	func (t *T) report() {
	tstr := fmt.Sprintf("(%.2f seconds)", t.duration.Seconds())
	format := "--- %s: %s %s\n%s"
	if t.Failed() {
	fmt.Printf(format, "FAIL", t.name, tstr, t.output)
	} else if *chatty {
	if t.Skipped() {
	fmt.Printf(format, "SKIP", t.name, tstr, t.output)
	} else {
	fmt.Printf(format, "PASS", t.name, tstr, t.output)
	}
	}
	}

	func RunTests(matchString func(pat, str string) (bool, error), tests []InternalTest) (ok bool) {
	ok = true
	if len(tests) == 0 && !haveExamples {
	fmt.Fprintln(os.Stderr, "testing: warning: no tests to run")
	return
	}
	for _, procs := range cpuList {
	runtime.GOMAXPROCS(procs)
	// We build a new channel tree for each run of the loop.
	// collector merges in one channel all the upstream signals from parallel tests.
	// If all tests pump to the same channel, a bug can occur where a test
	// kicks off a goroutine that Fails, yet the test still delivers a completion signal,
	// which skews the counting.
	var collector = make(chan interface{})

	numParallel := 0
	startParallel := make(chan bool)

	for i := 0; i < len(tests); i++ {
	matched, err := matchString(*match, tests[i].Name)
	if err != nil {
	fmt.Fprintf(os.Stderr, "testing: invalid regexp for -test.run: %s\n", err)
	os.Exit(1)
	}
	if !matched {
	continue
	}
	testName := tests[i].Name
	if procs != 1 {
	testName = fmt.Sprintf("%s-%d", tests[i].Name, procs)
	}
	t := &T{
	common: common{
	signal: make(chan interface{}),
	},
	name: testName,
	startParallel: startParallel,
	}
	t.self = t
	if *chatty {
	fmt.Printf("=== RUN %s\n", t.name)
	}
	go tRunner(t, &tests[i])
	out := (<-t.signal).(*T)
	if out == nil { // Parallel run.
	go func() {
	collector <- <-t.signal
	}()
	numParallel++
	continue
	}
	t.report()
	ok = ok && !out.Failed()
	}

	running := 0
	for numParallel+running > 0 {
	if running < *parallel && numParallel > 0 {
	startParallel <- true
	running++
	numParallel--
	continue
	}
	t := (<-collector).(*T)
	t.report()
	ok = ok && !t.Failed()
	running--
	}
	}
	return
	}

	// before runs before all testing.
	func before() {
	if *memProfileRate > 0 {
	runtime.MemProfileRate = *memProfileRate
	}
	if *cpuProfile != "" {
	f, err := os.Create(toOutputDir(*cpuProfile))
	if err != nil {
	fmt.Fprintf(os.Stderr, "testing: %s", err)
	return
	}
	if err := pprof.StartCPUProfile(f); err != nil {
	fmt.Fprintf(os.Stderr, "testing: can't start cpu profile: %s", err)
	f.Close()
	return
	}
	// Could save f so after can call f.Close; not worth the effort.
	}
	if blockProfile != "" && blockProfileRate >= 0 {
	runtime.SetBlockProfileRate(*blockProfileRate)
	}
	if *coverProfile != "" && cover.Mode == "" {
	fmt.Fprintf(os.Stderr, "testing: cannot use -test.coverprofile because test binary was not built with coverage enabled\n")
	os.Exit(2)
	}
	}

	// after runs after all testing.
	func after() {
	if *cpuProfile != "" {
	pprof.StopCPUProfile() // flushes profile to disk
	}
	if *memProfile != "" {
	f, err := os.Create(toOutputDir(*memProfile))
	if err != nil {
	fmt.Fprintf(os.Stderr, "testing: %s\n", err)
	os.Exit(2)
	}
	if err = pprof.WriteHeapProfile(f); err != nil {
	fmt.Fprintf(os.Stderr, "testing: can't write %s: %s\n", *memProfile, err)
	os.Exit(2)
	}
	f.Close()
	}
	if blockProfile != "" && blockProfileRate >= 0 {
	f, err := os.Create(toOutputDir(*blockProfile))
	if err != nil {
	fmt.Fprintf(os.Stderr, "testing: %s\n", err)
	os.Exit(2)
	}
	if err = pprof.Lookup("block").WriteTo(f, 0); err != nil {
	fmt.Fprintf(os.Stderr, "testing: can't write %s: %s\n", *blockProfile, err)
	os.Exit(2)
	}
	f.Close()
	}
	if cover.Mode != "" {
	coverReport()
	}
	}

	// toOutputDir returns the file name relocated, if required, to outputDir.
	// Simple implementation to avoid pulling in path/filepath.
	func toOutputDir(path string) string {
	if *outputDir == "" \|\| path == "" {
	return path
	}
	if runtime.GOOS == "windows" {
	// On Windows, it's clumsy, but we can be almost always correct
	// by just looking for a drive letter and a colon.
	// Absolute paths always have a drive letter (ignoring UNC).
	// Problem: if path == "C:A" and outputdir == "C:\Go" it's unclear
	// what to do, but even then path/filepath doesn't help.
	// TODO: Worth doing better? Probably not, because we're here only
	// under the management of go test.
	if len(path) >= 2 {
	letter, colon := path[0], path[1]
	if ('a' <= letter && letter <= 'z' \|\| 'A' <= letter && letter <= 'Z') && colon == ':' {
	// If path starts with a drive letter we're stuck with it regardless.
	return path
	}
	}
	}
	if os.IsPathSeparator(path[0]) {
	return path
	}
	return fmt.Sprintf("%s%c%s", *outputDir, os.PathSeparator, path)
	}

	var timer *time.Timer

	// startAlarm starts an alarm if requested.
	func startAlarm() {
	if *timeout > 0 {
	timer = time.AfterFunc(*timeout, func() {
	panic(fmt.Sprintf("test timed out after %v", *timeout))
	})
	}
	}

	// stopAlarm turns off the alarm.
	func stopAlarm() {
	if *timeout > 0 {
	timer.Stop()
	}
	}

	func parseCpuList() {
	for _, val := range strings.Split(*cpuListStr, ",") {
	val = strings.TrimSpace(val)
	if val == "" {
	continue
	}
	cpu, err := strconv.Atoi(val)
	if err != nil \|\| cpu <= 0 {
	fmt.Fprintf(os.Stderr, "testing: invalid value %q for -test.cpu\n", val)
	os.Exit(1)
	}
	cpuList = append(cpuList, cpu)
	}
	if cpuList == nil {
	cpuList = append(cpuList, runtime.GOMAXPROCS(-1))
	}
	}