addressing some of @josenavas comments

Author: antgonza

qiita_db/study.py

@@ -364,6 +364,9 @@ def delete(cls, id_):
         """
         cls._check_subclass()
 
+        # checking that the id_ exists
+        cls(id_)
+
         conn_handler = SQLConnectionHandler()
         if exists_table('sample_%d' % id_, conn_handler):
             raise QiitaDBError('Study "%s" cannot be erased because it has a '

qiita_db/test/test_study.py

@@ -12,7 +12,8 @@
 from qiita_db.data import RawData
 from qiita_db.util import convert_to_id
 from qiita_db.exceptions import (
-    QiitaDBColumnError, QiitaDBStatusError, QiitaDBError)
+    QiitaDBColumnError, QiitaDBStatusError, QiitaDBError,
+    QiitaDBUnknownIDError)
 
 # -----------------------------------------------------------------------------
 # Copyright (c) 2014--, The Qiita Development Team.
@@ -448,6 +449,9 @@ def test_delete(self):
         with self.assertRaises(QiitaDBError):
             Study.delete(1)
 
+        with self.assertRaises(QiitaDBUnknownIDError):
+            Study.delete(41)
+
     def test_retrieve_title(self):
         self.assertEqual(self.study.title, 'Identification of the Microbiomes'
                          ' for Cannabis Soils')