api: add __reversed__ for RevisionsIterator which allows to use rever…

…sed operator

 *Allows for proper use pf reversed operator with new implementation of __getitem__ if there are gaps in revision numbers

invenio_records/api.py

@@ -421,3 +421,8 @@ def __contains__(self, revision_id):
             return True
         except IndexError:
             return False
+
+    def __reversed__(self):
+        """Allows to use reversed operator."""
+        for version_index in range(self.model.versions.count()):
+            yield RecordRevision(self.model.versions[-(version_index+1)])

tests/test_api.py

@@ -431,3 +431,22 @@ def test_validate_partial(app, db):
         record['a'] = 1
         with pytest.raises(ValidationError) as exc_info:
             record.commit(validator=PartialDraft4Validator)
+
+
+def test_reversed_works_for_revisions(app, db):
+    record = Record.create({'title': 'test 1'})
+    db.session.commit()
+
+    record['title'] = "test 2"
+    record.commit()
+    record['title'] = "Test 3"
+    db.session.commit()
+
+    record['title'] = "test 4"
+    record.commit()
+    db.session.commit()
+
+    reversed_revisions = list(reversed(record.revisions))
+    reversed_revisions[0].revision_id == 3
+    reversed_revisions[1].revision_id == 1
+    reversed_revisions[2].revision_id == 0