Adding script to enable clearing datastore.

CONTRIBUTING.rst

@@ -209,6 +209,12 @@ Running Regression Tests
 
    $ python regression/populate_datastore.py
 
+- If you make a mistake during development (i.e. a failing test that
+  prevents clean-up) you can clear all regression data from your
+  datastore instance via::
+
+   $ python regression/clear_datastore.py
+
 Test Coverage
 -------------
 

regression/clear_datastore.py

@@ -0,0 +1,57 @@
+"""Script to populate datastore with regression test data."""
+
+
+# This assumes the command is being run via tox hence the
+# repository root is the current directory.
+from regression import regression_utils
+
+
+FETCH_MAX = 20
+ALL_KINDS = [
+    'Character',
+    'Company',
+    'Kind',
+    'Person',
+    'Post',
+]
+
+
+def remove_kind(dataset, kind):
+    dataset_id = dataset.id()
+    connection = dataset.connection()
+
+    with dataset.transaction():
+        query = dataset.query(kind=kind).limit(
+            FETCH_MAX).projection(['__key__'])
+        results = []
+        more_results = True
+        while more_results:
+            # Make new query.
+            if query._cursor is not None:
+                query = query.with_cursor(query._cursor)
+
+            curr_results = query.fetch()
+            results.extend(curr_results)
+
+            more_results = len(curr_results) == FETCH_MAX
+
+        # Now that we have all results, we seek to delete.
+        key_pbs = [entity.key().to_protobuf() for entity in results]
+        connection.delete_entities(dataset_id, key_pbs)
+
+
+def remove_all_entities():
+    print 'This command will remove all entities for the following kinds:'
+    print '\n'.join(['- ' + val for val in ALL_KINDS])
+    response = raw_input('Is this OK [y/n]? ')
+    if response.lower() != 'y':
+        print 'Doing nothing.'
+        return
+
+    dataset = regression_utils.get_dataset()
+    for kind in ALL_KINDS:
+        remove_kind(dataset, kind)
+
+
+if __name__ == '__main__':
+    remove_all_entities()