[release-branch.go1.21] runtime: don't let the tests leave core files behind

Also add a check that we didn't leave any core files behind.

For #65476.
Fixes #65478. 

Change-Id: I30444ef43ad1a8cc1cacd3b75280f2128e104939
Reviewed-on: https://go-review.googlesource.com/c/go/+/525175
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Keith Randall <khr@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@golang.org>
(cherry picked from commit cffdfe8d2c)
Reviewed-on: https://go-review.googlesource.com/c/go/+/560896

src/runtime/crash_test.go

@@ -24,10 +24,21 @@ import (
 var toRemove []string
 
 func TestMain(m *testing.M) {
+	_, coreErrBefore := os.Stat("core")
+
 	status := m.Run()
 	for _, file := range toRemove {
 		os.RemoveAll(file)
 	}
+
+	_, coreErrAfter := os.Stat("core")
+	if coreErrBefore != nil && coreErrAfter == nil {
+		fmt.Fprintln(os.Stderr, "runtime.test: some test left a core file behind")
+		if status == 0 {
+			status = 1
+		}
+	}
+
 	os.Exit(status)
 }
 

src/runtime/crash_unix_test.go

@@ -91,6 +91,7 @@ func TestCrashDumpsAllThreads(t *testing.T) {
 
 	cmd := testenv.Command(t, exe, "CrashDumpsAllThreads")
 	cmd = testenv.CleanCmdEnv(cmd)
+	cmd.Dir = t.TempDir() // put any core file in tempdir
 	cmd.Env = append(cmd.Env,
 		"GOTRACEBACK=crash",
 		// Set GOGC=off. Because of golang.org/issue/10958, the tight
@@ -164,6 +165,7 @@ func TestPanicSystemstack(t *testing.T) {
 	t.Parallel()
 	cmd := exec.Command(os.Args[0], "testPanicSystemstackInternal")
 	cmd = testenv.CleanCmdEnv(cmd)
+	cmd.Dir = t.TempDir() // put any core file in tempdir
 	cmd.Env = append(cmd.Env, "GOTRACEBACK=crash")
 	pr, pw, err := os.Pipe()
 	if err != nil {

src/runtime/testdata/testprogcgo/threadprof.go

@@ -92,7 +92,9 @@ func CgoExternalThreadSignal() {
 		return
 	}
 
-	out, err := exec.Command(os.Args[0], "CgoExternalThreadSignal", "crash").CombinedOutput()
+	cmd := exec.Command(os.Args[0], "CgoExternalThreadSignal", "crash")
+	cmd.Dir = os.TempDir() // put any core file in tempdir
+	out, err := cmd.CombinedOutput()
 	if err == nil {
 		fmt.Println("C signal did not crash as expected")
 		fmt.Printf("\n%s\n", out)