Output message if no data files are found for date (#21)

leanplum_data_export/export.py

@@ -3,6 +3,7 @@ import json
 import logging
 import os
 import re
+import sys
 import tempfile
 from pathlib import Path
 from typing import Dict, List, Set
@@ -81,6 +82,13 @@ class LeanplumExporter(object):
                 **continuation_token,
                 **max_keys,
             )
+
+            try:
+                assert object_list["KeyCount"] > 0
+            except AssertionError:
+                print(f"Error: No data files found for date {date}", file=sys.stderr)
+                raise
+
             data_file_keys.extend([content["Key"] for content in object_list["Contents"]
                                    if filename_re.fullmatch(content["Key"])])
 

tests/test_leanplum_export.py

@@ -298,6 +298,21 @@ class TestStreamingExporter(object):
         }
         assert expected == set(retrieved_keys)
 
+    @mock_s3
+    def test_get_files_no_files(self):
+        # can't use fixture because it's instantiated before moto3e
+        exporter = LeanplumExporter("projectId")
+
+        bucket_name = "bucket"
+        date = "20200601"
+        prefix = "firefox"
+
+        s3_client = boto3.client("s3")
+        s3_client.create_bucket(Bucket=bucket_name)
+
+        with pytest.raises(AssertionError):
+            exporter.get_files(date, bucket_name, prefix)
+
     @mock_s3
     def test_get_files_pagination(self):
         # can't use fixture because it's instantiated before moto