Improve SessionNew tests

pwd/storage_mock_test.go

@@ -1,11 +1,19 @@
 package pwd
 
 type mockStorage struct {
+	save func() error
+	load func() error
 }
 
 func (m *mockStorage) Save() error {
+	if m.save != nil {
+		return m.save()
+	}
 	return nil
 }
 func (m *mockStorage) Load() error {
+	if m.load != nil {
+		return m.load()
+	}
 	return nil
 }