[#139] test: Add test storage implementation

This aims to reduce the usage of chmod hackery to induce or simulate
OS-related failures.

Signed-off-by: Alejandro Lopez <a.lopez@yadro.com>

pkg/local_object_storage/writecache/util.go

@@ -1,6 +1,7 @@
 package writecache
 
 import (
+	"io/fs"
 	"os"
 	"path/filepath"
 	"time"
@@ -9,10 +10,11 @@ import (
 )
 
 // OpenDB opens BoltDB instance for write-cache. Opens in read-only mode if ro is true.
-func OpenDB(p string, ro bool) (*bbolt.DB, error) {
+func OpenDB(p string, ro bool, openFile func(string, int, fs.FileMode) (*os.File, error)) (*bbolt.DB, error) {
 	return bbolt.Open(filepath.Join(p, dbName), os.ModePerm, &bbolt.Options{
 		NoFreelistSync: true,
 		ReadOnly:       ro,
 		Timeout:        100 * time.Millisecond,
+		OpenFile:       openFile,
 	})
 }