1 files changed, 27 insertions, 5 deletions
diff --git a/libgo/go/testing/testing.go b/libgo/go/testing/testing.go
index 9ec3869768c..bcbe8f15c55 100644
--- a/libgo/go/testing/testing.go
+++ b/libgo/go/testing/testing.go
@@ -149,6 +149,7 @@ import (
 	"fmt"
 	"os"
 	"runtime"
+	"runtime/debug"
 	"runtime/pprof"
 	"strconv"
 	"strings"
@@ -281,9 +282,18 @@ 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.
+//
+// A test ends when its Test function returns or calls any of the methods
+// FailNow, Fatal, Fatalf, SkipNow, Skip, or Skipf. Those methods, as well as
+// the Parallel method, must be called only from the goroutine running the
+// Test function.
+//
+// The other reporting methods, such as the variations of Log and Error,
+// may be called simultaneously from multiple goroutines.
 type T struct {
 	common
-	name          string    // Name of test.
+	name          string // Name of test.
+	isParallel    bool
 	startParallel chan bool // Parallel tests will wait on this.
 }
 
@@ -417,10 +427,17 @@ func (c *common) Skipped() bool {
 // Parallel signals that this test is to be run in parallel with (and only with)
 // other parallel tests.
 func (t *T) Parallel() {
+	if t.isParallel {
+		panic("testing: t.Parallel called multiple times")
+	}
+	t.isParallel = true
+
+	// We don't want to include the time we spend waiting for serial tests
+	// in the test duration. Record the elapsed time thus far and reset the
+	// timer afterwards.
+	t.duration += time.Since(t.start)
 	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()
 }
 
@@ -437,7 +454,7 @@ func tRunner(t *T, test *InternalTest) {
 	// 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)
+		t.duration += time.Now().Sub(t.start)
 		// If the test panicked, print any test output before dying.
 		err := recover()
 		if !t.finished && err == nil {
@@ -484,7 +501,11 @@ func MainStart(matchString func(pat, str string) (bool, error), tests []Internal
 
 // Run runs the tests. It returns an exit code to pass to os.Exit.
 func (m *M) Run() int {
-	flag.Parse()
+	// TestMain may have already called flag.Parse.
+	if !flag.Parsed() {
+		flag.Parse()
+	}
+
 	parseCpuList()
 
 	before()
@@ -704,6 +725,7 @@ var timer *time.Timer
 func startAlarm() {
 	if *timeout > 0 {
 		timer = time.AfterFunc(*timeout, func() {
+			debug.SetTraceback("all")
 			panic(fmt.Sprintf("test timed out after %v", *timeout))
 		})
 	}