cmd/go/internal/test: pass default timeout to test programs even if it is not given from command line

Make 'go test' command to pass the default timeout (10m) to test programs even if the value is not given from command line.

Fixes #28147

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

@@ -484,8 +484,9 @@ var (
 	pkgArgs          []string
 	pkgs             []*load.Package
 
-	testKillTimeout = 10 * time.Minute
+	testActualTimeout = 10 * time.Minute                  // actual timeout which is passed to tests
-	testCacheExpire time.Time // ignore cached test results before this time
+	testKillTimeout   = testActualTimeout + 1*time.Minute // backup alarm
+	testCacheExpire   time.Time                           // ignore cached test results before this time
 )
 
 // testVetFlags is the list of flags to pass to vet when invoked automatically during go test.
@@ -552,13 +553,21 @@ func runTest(cmd *base.Command, args []string) {
 	// the test wedges with a goroutine spinning and its background
 	// timer does not get a chance to fire.
 	if dt, err := time.ParseDuration(testTimeout); err == nil && dt > 0 {
-		testKillTimeout = dt + 1*time.Minute
+		testActualTimeout = dt
+		testKillTimeout = testActualTimeout + 1*time.Minute
 	} else if err == nil && dt == 0 {
 		// An explicit zero disables the test timeout.
+		// No timeout is passed to tests.
 		// Let it have one century (almost) before we kill it.
+		testActualTimeout = -1
 		testKillTimeout = 100 * 365 * 24 * time.Hour
 	}
 
+	// Pass timeout to tests if it exists.
+	if testActualTimeout > 0 {
+		testArgs = append(testArgs, "-test.timeout="+testActualTimeout.String())
+	}
+
 	// show passing test output (after buffering) with -v flag.
 	// must buffer because tests are running in parallel, and
 	// otherwise the output will get mixed.

src/cmd/go/testdata/script/test_timeout.txt

@@ -0,0 +1,21 @@
+env GO111MODULE=off
+cd a
+
+# No timeout is passed via 'go test' command.
+go test -v
+stdout '10m0s'
+
+# Timeout is passed via 'go test' command.
+go test -v -timeout 30m
+stdout '30m0s'
+
+-- a/timeout_test.go --
+package t
+import (
+	"flag"
+	"fmt"
+	"testing"
+)
+func TestTimeout(t *testing.T) {
+	fmt.Println(flag.Lookup("test.timeout").Value.String())
+}