lint: enable usetesting linter (#7322)

Enable the usetesting linter in golangci.yml configuration to
enforce proper testing practices. Replace manual temporary
directory and file creation with t.TempDir() in test files.

This improves test reliability by ensuring proper cleanup and
follows Go testing best practices.

Signed-off-by: Ville Vesilehto <ville@vesilehto.fi>

.golangci.yml

@@ -8,6 +8,7 @@ linters:
     - unconvert
     - unused
     - whitespace
+    - usetesting
   exclusions:
     generated: lax
     presets:

plugin/file/tree/print_test.go

@@ -70,7 +70,7 @@ func TestPrint(t *testing.T) {
 
 	*/
 
-	f, err := os.CreateTemp("", "print_test_tmp")
+	f, err := os.CreateTemp(t.TempDir(), "print_test_tmp")
 	if err != nil {
 		t.Error(err)
 	}

plugin/pkg/tls/tls_test.go

@@ -1,7 +1,6 @@
 package tls
 
 import (
-	"os"
 	"path/filepath"
 	"testing"
 
@@ -79,15 +78,8 @@ func TestNewTLSConfigFromArgs(t *testing.T) {
 
 func TestNewTLSConfigFromArgsWithRoot(t *testing.T) {
 	cert, key, ca := getPEMFiles(t)
-	tempDir, err := os.MkdirTemp("", "go-test-pemfiles")
+	tempDir := t.TempDir()
-	defer func() {
+
-		if err := os.RemoveAll(tempDir); err != nil {
-			t.Error("failed to clean up temporary directory", err)
-		}
-	}()
-	if err != nil {
-		t.Error("failed to create temporary directory", err)
-	}
 	root := tempDir
 	args := []string{cert, key, ca}
 	for i := range args {

plugin/root/root_test.go

@@ -23,7 +23,7 @@ func TestRoot(t *testing.T) {
 
 	nonExistingDir := filepath.Join(existingDirPath, "highly_unlikely_to_exist_dir")
 
-	existingFile, err := os.CreateTemp("", "root_test")
+	existingFile, err := os.CreateTemp(t.TempDir(), "root_test")
 	if err != nil {
 		t.Fatalf("BeforeTest: Failed to create temp file for testing! Error was: %v", err)
 	}