Draft: Added prometheus metrics

tests/test_writer.py

@@ -8,6 +8,8 @@ from unittest.mock import patch, ANY, create_autospec
 
 from minio import Minio
 
+from prometheus_client.registry import REGISTRY
+
 from lofar_stingray.writer import Block, Storage
 
 
@@ -17,6 +19,14 @@ class TestStorage(TestCase):
     def setUp(self):
         self.mock_minio = create_autospec(Minio)
 
+        # Clear all metrics to make sure we don't register the same one twice
+        # between tests (the library forbids it).
+        #
+        # Unfortunately, Metrics draw copies of prometheus_client.registry.REGISTRY,
+        # and that does not provide a public interface to query the registered collectors.
+        for collector in list(REGISTRY._collector_to_names.keys()):
+            REGISTRY.unregister(collector)
+
     def test_create_bucket_if_not_exists(self):
         """Test if bucket is created if not exists"""
         self.mock_minio.bucket_exists.return_value = False