testing: only capture stdout when running examples

Fixes #4550.

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/6973048

src/cmd/go/doc.go

@@ -76,7 +76,13 @@ The build flags are shared by the build, install, run, and test commands:
 		do not delete it when exiting.
 	-x
 		print the commands.
+	-race
+		enable data race detection.
+		Currently supported only on linux/amd64,
+		darwin/amd64 and windows/amd64.
 
+	-ccflags 'arg list'
+		arguments to pass on each 5c, 6c, or 8c compiler invocation
 	-compiler name
 		name of compiler to use, as in runtime.Compiler (gccgo or gc)
 	-gccgoflags 'arg list'
@@ -121,6 +127,7 @@ source directories corresponding to the import paths:
 	DIR(.exe)        from go build
 	DIR.test(.exe)   from go test -c
 	MAINFILE(.exe)   from go build MAINFILE.go
+	*.so             from SWIG
 
 In the list, DIR represents the final path element of the
 directory, and MAINFILE is the base name of any Go source
@@ -276,10 +283,10 @@ The default output shows the package import path:
     code.google.com/p/goauth2/oauth
     code.google.com/p/sqlite
 
-The -f flag specifies an alternate format for the list,
-using the syntax of package template.  The default output
-is equivalent to -f '{{.ImportPath}}'.  The struct
-being passed to the template is:
+The -f flag specifies an alternate format for the list, using the
+syntax of package template.  The default output is equivalent to -f
+'{{.ImportPath}}'.  One extra template function is available, "join",
+which calls strings.Join. The struct being passed to the template is:
 
     type Package struct {
         Dir        string // directory containing package sources
@@ -679,6 +686,9 @@ directory containing the package sources, has its own flags:
 	    Run benchmarks matching the regular expression.
 	    By default, no benchmarks run.
 
+	-test.benchmem
+	    Print memory allocation statistics for benchmarks.
+
 	-test.cpuprofile cpu.out
 	    Write a CPU profile to the specified file before exiting.
 
@@ -694,6 +704,18 @@ directory containing the package sources, has its own flags:
 	    garbage collector, provided the test can run in the available
 	    memory without garbage collection.
 
+	-test.blockprofile block.out
+	    Write a goroutine blocking profile to the specified file
+	    when all tests are complete.
+
+	-test.blockprofilerate n
+	    Control the detail provided in goroutine blocking profiles by setting
+	    runtime.BlockProfileRate to n.  See 'godoc runtime BlockProfileRate'.
+	    The profiler aims to sample, on average, one blocking event every
+	    n nanoseconds the program spends blocked.  By default,
+	    if -test.blockprofile is set without this flag, all blocking events
+	    are recorded, equivalent to -test.blockprofilerate=1.
+
 	-test.parallel n
 	    Allow parallel execution of test functions that call t.Parallel.
 	    The value of this flag is the maximum number of tests to run

src/cmd/go/test.go

@@ -175,8 +175,8 @@ A benchmark function is one named BenchmarkXXX and should have the signature,
 
 	func BenchmarkXXX(b *testing.B) { ... }
 
-An example function is similar to a test function but, instead of using *testing.T
-to report success or failure, prints output to os.Stdout and os.Stderr.
+An example function is similar to a test function but, instead of using
+*testing.T to report success or failure, prints output to os.Stdout.
 That output is compared against the function's "Output:" comment, which
 must be the last comment in the function body (see example below). An
 example with no such comment, or with no text after "Output:" is compiled

src/pkg/testing/example.go

@@ -24,7 +24,7 @@ func RunExamples(matchString func(pat, str string) (bool, error), examples []Int
 
 	var eg InternalExample
 
-	stdout, stderr := os.Stdout, os.Stderr
+	stdout := os.Stdout
 
 	for _, eg = range examples {
 		matched, err := matchString(*match, eg.Name)
@@ -39,19 +39,19 @@ func RunExamples(matchString func(pat, str string) (bool, error), examples []Int
 			fmt.Printf("=== RUN: %s\n", eg.Name)
 		}
 
-		// capture stdout and stderr
+		// capture stdout
 		r, w, err := os.Pipe()
 		if err != nil {
 			fmt.Fprintln(os.Stderr, err)
 			os.Exit(1)
 		}
-		os.Stdout, os.Stderr = w, w
+		os.Stdout = w
 		outC := make(chan string)
 		go func() {
 			buf := new(bytes.Buffer)
 			_, err := io.Copy(buf, r)
 			if err != nil {
-				fmt.Fprintf(stderr, "testing: copying pipe: %v\n", err)
+				fmt.Fprintf(os.Stderr, "testing: copying pipe: %v\n", err)
 				os.Exit(1)
 			}
 			outC <- buf.String()
@@ -62,9 +62,9 @@ func RunExamples(matchString func(pat, str string) (bool, error), examples []Int
 		eg.F()
 		dt := time.Now().Sub(t0)
 
-		// close pipe, restore stdout/stderr, get output
+		// close pipe, restore stdout, get output
 		w.Close()
-		os.Stdout, os.Stderr = stdout, stderr
+		os.Stdout = stdout
 		out := <-outC
 
 		// report any errors