testing: clarify -timeout flag

Fixes #20090

Change-Id: I881607e55cd946a703e74a7d8ae2bbde67546510
Reviewed-on: https://go-review.googlesource.com/45816Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/go/alldocs.go

@@ -1489,8 +1489,9 @@
 // 	    the Go tree can run a sanity check but not spend time running
 // 	    exhaustive tests.
 //
-// 	-timeout t
-// 	    If a test runs longer than t, panic.
+// 	-timeout d
+// 	    If the cumulative test time for a package runs longer than
+// 	    duration d, panic. Timeout is disabled if set to 0.
 // 	    The default is 10 minutes (10m).
 //
 // 	-v

src/cmd/go/internal/test/test.go

@@ -214,8 +214,9 @@ const testFlag2 = `
 	    the Go tree can run a sanity check but not spend time running
 	    exhaustive tests.
 
-	-timeout t
-	    If a test runs longer than t, panic.
+	-timeout d
+	    If the cumulative test time for a package runs longer than
+	    duration d, panic. Timeout is disabled if set to 0.
 	    The default is 10 minutes (10m).
 
 	-v

src/testing/testing.go

@@ -265,7 +265,7 @@ var (
 	mutexProfile         = flag.String("test.mutexprofile", "", "write a mutex contention profile to the named file after execution")
 	mutexProfileFraction = flag.Int("test.mutexprofilefraction", 1, "if >= 0, calls runtime.SetMutexProfileFraction()")
 	traceFile            = flag.String("test.trace", "", "write an execution trace to `file`")
-	timeout              = flag.Duration("test.timeout", 0, "fail test binary execution after duration `d` (0 means unlimited)")
+	timeout              = flag.Duration("test.timeout", 0, "panic test binary after duration `d` (0 means unlimited)")
 	cpuListStr           = flag.String("test.cpu", "", "comma-separated `list` of cpu counts to run each test with")
 	parallel             = flag.Int("test.parallel", runtime.GOMAXPROCS(0), "run at most `n` tests in parallel")