cmd/go: terminate TestScript commands more aggressively when the test times out

- Avoid starting subprocesses when the test is already very close to
  timing out. The overhead of starting and stopping processes may
  cause the test to exceed its deadline even if each individual
  process is signaled soon after it is started.

- If a command does not shut down quickly enough after receiving
  os.Interrupt, send it os.Kill using the same style of grace period
  as in CL 228438.

- Fail the test if a background command whose exit status is not
  ignored is left running at the end of the test. We have no reliable
  way to distinguish a failure due to the termination signal from an
  unexpected failure, and the termination signal varies across
  platforms (so may cause failure on one platform but success on
  another).

For #38797

Change-Id: I767898cf551dca45579bf01a9d1bb312e12d6193
Reviewed-on: https://go-review.googlesource.com/c/go/+/233526
Run-TryBot: Bryan C. Mills <[email protected]>
Reviewed-by: Jay Conrod <[email protected]>

Author: Bryan C. Mills

src/cmd/go/go_test.go

@@ -6,7 +6,6 @@ package main_test
 
 import (
 	"bytes"
-	"context"
 	"debug/elf"
 	"debug/macho"
 	"debug/pe"
@@ -114,12 +113,6 @@ var testGo string
 var testTmpDir string
 var testBin string
 
-// testCtx is canceled when the test binary is about to time out.
-//
-// If https://golang.org/issue/28135 is accepted, uses of this variable in test
-// functions should be replaced by t.Context().
-var testCtx = context.Background()
-
 // The TestMain function creates a go command for testing purposes and
 // deletes it after the tests have been run.
 func TestMain(m *testing.M) {
@@ -135,19 +128,6 @@ func TestMain(m *testing.M) {
 
 	flag.Parse()
 
-	timeoutFlag := flag.Lookup("test.timeout")
-	if timeoutFlag != nil {
-		// TODO(golang.org/issue/28147): The go command does not pass the
-		// test.timeout flag unless either -timeout or -test.timeout is explicitly
-		// set on the command line.
-		if d := timeoutFlag.Value.(flag.Getter).Get().(time.Duration); d != 0 {
-			aBitShorter := d * 95 / 100
-			var cancel context.CancelFunc
-			testCtx, cancel = context.WithTimeout(testCtx, aBitShorter)
-			defer cancel()
-		}
-	}
-
 	if *proxyAddr != "" {
 		StartProxy()
 		select {}