config: fix panic on multiple Close() (#1374)

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

config/source/file/file_test.go

@@ -1,4 +1,4 @@
-package file
+package file_test
 
 import (
 	"fmt"
@@ -6,8 +6,37 @@ import (
 	"path/filepath"
 	"testing"
 	"time"
+
+	"github.com/micro/go-micro/v2/config"
+	"github.com/micro/go-micro/v2/config/source/file"
 )
 
+func TestConfig(t *testing.T) {
+	data := []byte(`{"foo": "bar"}`)
+	path := filepath.Join(os.TempDir(), fmt.Sprintf("file.%d", time.Now().UnixNano()))
+	fh, err := os.Create(path)
+	if err != nil {
+		t.Error(err)
+	}
+	defer func() {
+		fh.Close()
+		os.Remove(path)
+	}()
+	_, err = fh.Write(data)
+	if err != nil {
+		t.Error(err)
+	}
+
+	conf, err := config.NewConfig()
+	if err != nil {
+		t.Fatal(err)
+	}
+	conf.Load(file.NewSource(file.WithPath(path)))
+	// simulate multiple close
+	go conf.Close()
+	go conf.Close()
+}
+
 func TestFile(t *testing.T) {
 	data := []byte(`{"foo": "bar"}`)
 	path := filepath.Join(os.TempDir(), fmt.Sprintf("file.%d", time.Now().UnixNano()))
@@ -25,7 +54,7 @@ func TestFile(t *testing.T) {
 		t.Error(err)
 	}
 
-	f := NewSource(WithPath(path))
+	f := file.NewSource(file.WithPath(path))
 	c, err := f.Read()
 	if err != nil {
 		t.Error(err)