fixup add sample tests

Author: llucax

tests/metrics/test_sample.py

@@ -385,6 +385,8 @@ def test_metric_sample_from_proto(
     else:
         assert sample.value is None
 
-    mock_to_datetime.assert_called_once()
-    mock_enum_from_proto.assert_called_once()
-    mock_bounds_from_proto.assert_called_once()
+    mock_to_datetime.assert_called_once_with(timestamp)
+    mock_enum_from_proto.assert_called_once_with(metric_value, Metric)
+    mock_bounds_from_proto.assert_called_once_with(
+        bounds_pb2.Bounds(lower=-10.0, upper=10.0)
+    )