os: clean up tests

- Use testenv.Command instead of exec.Command to try to get more
  useful timeout behavior.

- Parallelize tests that appear not to require global state.
  (And add explanatory comments for a few that are not
  parallelizable for subtle reasons.)

- Consolidate some “Helper” tests with their parent tests.

- Use t.TempDir instead of os.MkdirTemp when appropriate.

- Factor out subtests for repeated test helpers.

For #36107.
Updates #22315.

Change-Id: Ic24b6957094dcd40908a59f48e44c8993729222b
Reviewed-on: https://go-review.googlesource.com/c/go/+/458015
Reviewed-by: Ian Lance Taylor <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Bryan Mills <[email protected]>
Auto-Submit: Bryan Mills <[email protected]>

Author: Bryan C. Mills

src/os/env_test.go

@@ -171,6 +171,8 @@ func TestLookupEnv(t *testing.T) {
 // Check that they are properly reported by LookupEnv and can be set by SetEnv.
 // See https://golang.org/issue/49886.
 func TestEnvironConsistency(t *testing.T) {
+	t.Parallel()
+
 	for _, kv := range Environ() {
 		i := strings.Index(kv, "=")
 		if i == 0 {

src/os/error_test.go

@@ -14,6 +14,8 @@ import (
 )
 
 func TestErrIsExist(t *testing.T) {
+	t.Parallel()
+
 	f, err := os.CreateTemp("", "_Go_ErrIsExist")
 	if err != nil {
 		t.Fatalf("open ErrIsExist tempfile: %s", err)
@@ -148,6 +150,8 @@ func TestIsPermission(t *testing.T) {
 }
 
 func TestErrPathNUL(t *testing.T) {
+	t.Parallel()
+
 	f, err := os.CreateTemp("", "_Go_ErrPathNUL\x00")
 	if err == nil {
 		f.Close()

src/os/exec_unix_test.go

@@ -14,11 +14,9 @@ import (
 
 func TestErrProcessDone(t *testing.T) {
 	testenv.MustHaveGoBuild(t)
-	path, err := testenv.GoTool()
-	if err != nil {
-		t.Errorf("finding go tool: %v", err)
-	}
-	p, err := StartProcess(path, []string{"go"}, &ProcAttr{})
+	t.Parallel()
+
+	p, err := StartProcess(testenv.GoToolPath(t), []string{"go"}, &ProcAttr{})
 	if err != nil {
 		t.Errorf("starting test process: %v", err)
 	}

src/os/executable_test.go

@@ -8,7 +8,6 @@ import (
 	"fmt"
 	"internal/testenv"
 	"os"
-	osexec "os/exec"
 	"path/filepath"
 	"runtime"
 	"testing"
@@ -18,6 +17,8 @@ const executable_EnvVar = "OSTEST_OUTPUT_EXECPATH"
 
 func TestExecutable(t *testing.T) {
 	testenv.MustHaveExec(t)
+	t.Parallel()
+
 	ep, err := os.Executable()
 	if err != nil {
 		t.Fatalf("Executable failed: %v", err)
@@ -29,18 +30,18 @@ func TestExecutable(t *testing.T) {
 		t.Fatalf("filepath.Rel: %v", err)
 	}
 
-	cmd := &osexec.Cmd{}
+	cmd := testenv.Command(t, fn, "-test.run=XXXX")
 	// make child start with a relative program path
 	cmd.Dir = dir
 	cmd.Path = fn
-	// forge argv[0] for child, so that we can verify we could correctly
-	// get real path of the executable without influenced by argv[0].
-	cmd.Args = []string{"-", "-test.run=XXXX"}
 	if runtime.GOOS == "openbsd" || runtime.GOOS == "aix" {
 		// OpenBSD and AIX rely on argv[0]
-		cmd.Args[0] = fn
+	} else {
+		// forge argv[0] for child, so that we can verify we could correctly
+		// get real path of the executable without influenced by argv[0].
+		cmd.Args[0] = "-"
 	}
-	cmd.Env = append(os.Environ(), fmt.Sprintf("%s=1", executable_EnvVar))
+	cmd.Env = append(cmd.Environ(), fmt.Sprintf("%s=1", executable_EnvVar))
 	out, err := cmd.CombinedOutput()
 	if err != nil {
 		t.Fatalf("exec(self) failed: %v", err)
@@ -95,6 +96,7 @@ func TestExecutableDeleted(t *testing.T) {
 	case "openbsd", "freebsd", "aix":
 		t.Skipf("%v does not support reading deleted binary name", runtime.GOOS)
 	}
+	t.Parallel()
 
 	dir := t.TempDir()