all: use T.TempDir to create temporary test directories (#24633)

This commit replaces ioutil.TempDir with t.TempDir in tests. The
directory created by t.TempDir is automatically removed when the test
and all its subtests complete.

Prior to this commit, temporary directory created using ioutil.TempDir
had to be removed manually by calling os.RemoveAll, which is omitted in
some tests. The error handling boilerplate e.g.

	defer func() {
		if err := os.RemoveAll(dir); err != nil {
			t.Fatal(err)
		}
	}

is also tedious, but t.TempDir handles this for us nicely.

Reference: https://pkg.go.dev/testing#T.TempDir
Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>

signer/core/api_test.go

@@ -20,7 +20,6 @@ import (
 	"bytes"
 	"context"
 	"fmt"
-	"io/ioutil"
 	"math/big"
 	"os"
 	"path/filepath"
@@ -109,11 +108,8 @@ func (ui *headlessUi) ShowInfo(message string) {
 }
 
 func tmpDirName(t *testing.T) string {
-	d, err := ioutil.TempDir("", "eth-keystore-test")
-	if err != nil {
-		t.Fatal(err)
-	}
-	d, err = filepath.EvalSymlinks(d)
+	d := t.TempDir()
+	d, err := filepath.EvalSymlinks(d)
 	if err != nil {
 		t.Fatal(err)
 	}

signer/fourbyte/fourbyte_test.go

@@ -18,7 +18,6 @@ package fourbyte
 
 import (
 	"fmt"
-	"io/ioutil"
 	"strings"
 	"testing"
 
@@ -57,10 +56,7 @@ func TestEmbeddedDatabase(t *testing.T) {
 // Tests that custom 4byte datasets can be handled too.
 func TestCustomDatabase(t *testing.T) {
 	// Create a new custom 4byte database with no embedded component
-	tmpdir, err := ioutil.TempDir("", "signer-4byte-test")
-	if err != nil {
-		t.Fatal(err)
-	}
+	tmpdir := t.TempDir()
 	filename := fmt.Sprintf("%s/4byte_custom.json", tmpdir)
 
 	db, err := NewWithFile(filename)

signer/storage/aes_gcm_storage_test.go

@@ -62,10 +62,7 @@ func TestFileStorage(t *testing.T) {
 			CipherText: common.Hex2Bytes("2df87baf86b5073ef1f03e3cc738de75b511400f5465bb0ddeacf47ae4dc267d"),
 		},
 	}
-	d, err := ioutil.TempDir("", "eth-encrypted-storage-test")
-	if err != nil {
-		t.Fatal(err)
-	}
+	d := t.TempDir()
 	stored := &AESEncryptedStorage{
 		filename: fmt.Sprintf("%v/vault.json", d),
 		key:      []byte("AES256Key-32Characters1234567890"),
@@ -95,10 +92,7 @@ func TestFileStorage(t *testing.T) {
 func TestEnd2End(t *testing.T) {
 	log.Root().SetHandler(log.LvlFilterHandler(log.Lvl(3), log.StreamHandler(colorable.NewColorableStderr(), log.TerminalFormat(true))))
 
-	d, err := ioutil.TempDir("", "eth-encrypted-storage-test")
-	if err != nil {
-		t.Fatal(err)
-	}
+	d := t.TempDir()
 
 	s1 := &AESEncryptedStorage{
 		filename: fmt.Sprintf("%v/vault.json", d),
@@ -120,10 +114,7 @@ func TestSwappedKeys(t *testing.T) {
 	// K1:V1, K2:V2 can be swapped into K1:V2, K2:V1
 	log.Root().SetHandler(log.LvlFilterHandler(log.Lvl(3), log.StreamHandler(colorable.NewColorableStderr(), log.TerminalFormat(true))))
 
-	d, err := ioutil.TempDir("", "eth-encrypted-storage-test")
-	if err != nil {
-		t.Fatal(err)
-	}
+	d := t.TempDir()
 
 	s1 := &AESEncryptedStorage{
 		filename: fmt.Sprintf("%v/vault.json", d),