testing: add -test.example flag to control execution of examples

Also, don't run examples if -test.run is set.

R=golang-dev, dsymonds
CC=golang-dev
https://golang.org/cl/5697069

src/cmd/go/test.go

@@ -99,6 +99,11 @@ directory containing the package sources, has its own flags:
 	    Run benchmarks matching the regular expression.
 	    By default, no benchmarks run.
 
+	-test.example pattern
+	    Run examples matching the regular expression.
+	    By default, all examples run, but if -test.run is set,
+	    no examples are run.
+
 	-test.cpuprofile cpu.out
 	    Write a CPU profile to the specified file before exiting.
 

src/cmd/go/testflag.go

@@ -28,6 +28,7 @@ var usageMessage = `Usage of go test:
   -benchtime=1: passes -test.benchtime to test
   -cpu="": passes -test.cpu to test
   -cpuprofile="": passes -test.cpuprofile to test
+  -example="": passes -test.example to test
   -memprofile="": passes -test.memprofile to test
   -memprofilerate=0: passes -test.memprofilerate to test
   -parallel=0: passes -test.parallel to test
@@ -67,6 +68,7 @@ var testFlagDefn = []*testFlagSpec{
 	{name: "benchtime", passToTest: true},
 	{name: "cpu", passToTest: true},
 	{name: "cpuprofile", passToTest: true},
+	{name: "example", passToTest: true},
 	{name: "memprofile", passToTest: true},
 	{name: "memprofilerate", passToTest: true},
 	{name: "parallel", passToTest: true},

src/pkg/testing/example.go

@@ -6,6 +6,7 @@ package testing
 
 import (
 	"bytes"
+	"flag"
 	"fmt"
 	"io"
 	"os"
@@ -13,13 +14,18 @@ import (
 	"time"
 )
 
+var matchExamples = flag.String("test.example", "", "regular expression to select examples to run")
+
 type InternalExample struct {
 	Name   string
 	F      func()
 	Output string
 }
 
-func RunExamples(examples []InternalExample) (ok bool) {
+func RunExamples(matchString func(pat, str string) (bool, error), examples []InternalExample) (ok bool) {
+	if *match != "" {
+		return // Don't run examples if testing is restricted: we're debugging.
+	}
 	ok = true
 
 	var eg InternalExample
@@ -27,6 +33,14 @@ func RunExamples(examples []InternalExample) (ok bool) {
 	stdout, stderr := os.Stdout, os.Stderr
 
 	for _, eg = range examples {
+		matched, err := matchString(*matchExamples, eg.Name)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "testing: invalid regexp for -test.example: %s\n", err)
+			os.Exit(1)
+		}
+		if !matched {
+			continue
+		}
 		if *chatty {
 			fmt.Printf("=== RUN: %s\n", eg.Name)
 		}

src/pkg/testing/testing.go

@@ -280,7 +280,7 @@ func Main(matchString func(pat, str string) (bool, error), tests []InternalTest,
 	before()
 	startAlarm()
 	testOk := RunTests(matchString, tests)
-	exampleOk := RunExamples(examples)
+	exampleOk := RunExamples(matchString, examples)
 	if !testOk || !exampleOk {
 		fmt.Println("FAIL")
 		os.Exit(1)