test: use `T.TempDir` to create temporary test directory (#21043)

A testing cleanup. 

This pull request replaces `os.MkdirTemp` with `t.TempDir`. We can use the `T.TempDir` function from the `testing` package to create temporary directory. The directory created by `T.TempDir` is automatically removed when the test and all its subtests complete. 

This saves us at least 2 lines (error check, and cleanup) on every instance, or in some cases adds cleanup that we forgot.

Reference: https://pkg.go.dev/testing#T.TempDir

```go
func TestFoo(t *testing.T) {
	// before
	tmpDir, err := os.MkdirTemp("", "")
	require.NoError(t, err)
	defer os.RemoveAll(tmpDir)

	// now
	tmpDir := t.TempDir()
}
```

Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>

3 files changed, 4 insertions, 28 deletions

diff --git a/modules/indexer/code/bleve_test.go b/modules/indexer/code/bleve_test.go
index 37ed2eb9f0..a34d54bc0e 100644
--- a/modules/indexer/code/bleve_test.go
+++ b/modules/indexer/code/bleve_test.go
@@ -5,11 +5,9 @@
 package code
 
 import (
-	"os"
 	"testing"
 
 	"code.gitea.io/gitea/models/unittest"
-	"code.gitea.io/gitea/modules/util"
 
 	"github.com/stretchr/testify/assert"
 )
@@ -17,13 +15,7 @@ import (
 func TestBleveIndexAndSearch(t *testing.T) {
 	unittest.PrepareTestEnv(t)
 
-	dir, err := os.MkdirTemp("", "bleve.index")
-	assert.NoError(t, err)
-	if err != nil {
-		assert.Fail(t, "Unable to create temporary directory")
-		return
-	}
-	defer util.RemoveAll(dir)
+	dir := t.TempDir()
 
 	idx, _, err := NewBleveIndexer(dir)
 	if err != nil {
diff --git a/modules/indexer/issues/bleve_test.go b/modules/indexer/issues/bleve_test.go
index 68a7831a3f..42d22f06a2 100644
--- a/modules/indexer/issues/bleve_test.go
+++ b/modules/indexer/issues/bleve_test.go
@@ -6,22 +6,13 @@ package issues
 
 import (
 	"context"
-	"os"
 	"testing"
 
-	"code.gitea.io/gitea/modules/util"
-
 	"github.com/stretchr/testify/assert"
 )
 
 func TestBleveIndexAndSearch(t *testing.T) {
-	dir, err := os.MkdirTemp("", "bleve.index")
-	assert.NoError(t, err)
-	if err != nil {
-		assert.Fail(t, "Unable to create temporary directory")
-		return
-	}
-	defer util.RemoveAll(dir)
+	dir := t.TempDir()
 	indexer := NewBleveIndexer(dir)
 	defer indexer.Close()
 
@@ -30,7 +21,7 @@ func TestBleveIndexAndSearch(t *testing.T) {
 		return
 	}
 
-	err = indexer.Index([]*IndexerData{
+	err := indexer.Index([]*IndexerData{
 		{
 			ID:      1,
 			RepoID:  2,
diff --git a/modules/indexer/issues/indexer_test.go b/modules/indexer/issues/indexer_test.go
index 6bafcbdf24..e8b9ff8370 100644
--- a/modules/indexer/issues/indexer_test.go
+++ b/modules/indexer/issues/indexer_test.go
@@ -6,7 +6,6 @@ package issues
 
 import (
 	"context"
-	"os"
 	"path"
 	"path/filepath"
 	"testing"
@@ -14,7 +13,6 @@ import (
 
 	"code.gitea.io/gitea/models/unittest"
 	"code.gitea.io/gitea/modules/setting"
-	"code.gitea.io/gitea/modules/util"
 
 	_ "code.gitea.io/gitea/models"
 
@@ -32,11 +30,7 @@ func TestBleveSearchIssues(t *testing.T) {
 	assert.NoError(t, unittest.PrepareTestDatabase())
 	setting.Cfg = ini.Empty()
 
-	tmpIndexerDir, err := os.MkdirTemp("", "issues-indexer")
-	if err != nil {
-		assert.Fail(t, "Unable to create temporary directory: %v", err)
-		return
-	}
+	tmpIndexerDir := t.TempDir()
 
 	setting.Cfg.Section("queue.issue_indexer").Key("DATADIR").MustString(path.Join(tmpIndexerDir, "issues.queue"))
 
@@ -44,7 +38,6 @@ func TestBleveSearchIssues(t *testing.T) {
 	setting.Indexer.IssuePath = path.Join(tmpIndexerDir, "issues.queue")
 	defer func() {
 		setting.Indexer.IssuePath = oldIssuePath
-		util.RemoveAll(tmpIndexerDir)
 	}()
 
 	setting.Indexer.IssueType = "bleve"