Fix tests and lint errors, plus a bit of refactor

tests/mock_share_repo.go

@@ -20,8 +20,12 @@ func (m *MockShareRepo) Save(entity interface{}) (string, error) {
 	if m.Error != nil {
 		return "", m.Error
 	}
-	m.Entity = entity
-	return "id", nil
+	s := entity.(*model.Share)
+	if s.ID == "" {
+		s.ID = "id"
+	}
+	m.Entity = s
+	return s.ID, nil
 }
 
 func (m *MockShareRepo) Update(id string, entity interface{}, cols ...string) error {
@@ -33,3 +37,10 @@ func (m *MockShareRepo) Update(id string, entity interface{}, cols ...string) er
 	m.Cols = cols
 	return nil
 }
+
+func (m *MockShareRepo) Exists(id string) (bool, error) {
+	if m.Error != nil {
+		return false, m.Error
+	}
+	return id == m.ID, nil
+}