fix empty results by returning dataframe with a null value (#3)

app/helper/prometheus.py

@@ -6,6 +6,7 @@
 from requests import RequestException
 from .logger import logger
 import pandas as pd
+import time
 
 
 class Prometheus:
@@ -30,4 +31,12 @@ def get_current_value(self, query) -> pd.DataFrame:
                 "non 200 response status code on query {}".format(query),
                 stack_info=True,
             )
+        # handle empty results as a dummy metric with current time and none value.
+        if len(result) == 0:
+            return MetricSnapshotDataFrame(
+                data={
+                    "metric": {"__name__": "dummy_metric"},
+                    "value": [time.time(), None],
+                }
+            )
         return MetricSnapshotDataFrame(result)

tests/test_main.py

@@ -1,20 +1,25 @@
 from unittest.mock import patch, Mock
 from app.main import main
 
+
 @patch(
     "app.helper.prometheus.PrometheusConnect.check_prometheus_connection",
     Mock(return_value=True),
 )
 @patch(
     "app.helper.prometheus.PrometheusConnect.custom_query",
+    # It uses two outputs for the prometheus: an ordinary and an empty result.
     Mock(
-        return_value=[
-            {
-                "metric": {"__name__": "dummy_metric"},
-                "value": [1708184035.052, "0.29875"],
-            }
-        ]
+        side_effect=[
+            [
+                {
+                    "metric": {"__name__": "dummy_metric"},
+                    "value": [1708184035.052, "0.29875"],
+                }
+            ],
+            [],
+        ],
     ),
 )
 def test_main():
-    main(config_path="tests/config.yaml", output_path="tests/output.json")
+    main(config_path="tests/config.yaml", output_path="tests/output.json")