added new merge_taglists() to moto.core.utils for merging lists of tags with precedence (ie. during rds2.create_snapshot)

moto/core/utils.py

@@ -286,3 +286,12 @@ def amzn_request_id(f):
         return status, headers, body
 
     return _wrapper
+
+
+def merge_taglists(taglist_a, taglist_b):
+    ''' Merges two tag lists into a single tag list with Keys in the second list taking precedence'''
+    tags_a = {t['Key']:t for t in taglist_a}
+    tags_b = {t['Key']:t for t in taglist_b}
+    merged_tags = tags_a.copy()
+    merged_tags.update(tags_b)
+    return merged_tags.values()

moto/rds2/models.py

@@ -13,6 +13,7 @@ from moto.compat import OrderedDict
 from moto.core import BaseBackend, BaseModel
 from moto.core.utils import get_random_hex
 from moto.core.utils import iso_8601_datetime_with_milliseconds
+from moto.core.utils import merge_taglists
 from moto.ec2.models import ec2_backends
 from .exceptions import (RDSClientError,
                          DBInstanceNotFoundError,
@@ -697,8 +698,8 @@ class RDS2Backend(BaseBackend):
             raise DBSnapshotAlreadyExistsError(db_snapshot_identifier)
         if len(self.snapshots) >= int(os.environ.get('MOTO_RDS_SNAPSHOT_LIMIT', '100')):
             raise SnapshotQuotaExceededError()
-        if not database.copy_tags_to_snapshot:
-            tags = None
+        if database.copy_tags_to_snapshot:
+            tags = merge_taglists(database.tags, tags)
         snapshot = Snapshot(database, db_snapshot_identifier, tags)
         self.snapshots[db_snapshot_identifier] = snapshot
         return snapshot