Add unit test for Metrics class

Author: steventux

manage_breast_screening/notifications/services/metrics.py

@@ -11,12 +11,11 @@
 
 class Metrics:
     def __init__(self, metric_name, metric_units, metric_description):
-        logger.exception("init Metrics")
         self.metric_name = metric_name
 
         try:
             exporter = AzureMonitorMetricExporter(
-                connection_string=os.environ["APPLICATIONINSIGHTS_CONNECTION_STRING"]
+                connection_string=os.getenv("APPLICATIONINSIGHTS_CONNECTION_STRING")
             )
             reader = PeriodicExportingMetricReader(exporter)
             metrics.set_meter_provider(MeterProvider(metric_readers=[reader]))

manage_breast_screening/notifications/tests/services/test_metrics.py

@@ -1,22 +1,79 @@
-from unittest.mock import patch
+from unittest.mock import MagicMock, patch
 
 import pytest
 
 from manage_breast_screening.notifications.services.metrics import Metrics
 
 
 class TestMetrics:
+    @pytest.fixture
+    def conn_string(self):
+        return "InstrumentationKey=00000000-0000-0000-0000-000000000000"
+
     @pytest.fixture(autouse=True)
-    def setup(self, monkeypatch):
-        monkeypatch.setenv(
-            "APPLICATIONINSIGHTS_CONNECTION_STRING",
-            "InstrumentationKey=00000000-0000-0000-0000-000000000000",
+    def setup(self, monkeypatch, conn_string):
+        monkeypatch.setenv("APPLICATIONINSIGHTS_CONNECTION_STRING", conn_string)
+
+    @patch(
+        "manage_breast_screening.notifications.services.metrics.AzureMonitorMetricExporter"
+    )
+    @patch(
+        "manage_breast_screening.notifications.services.metrics.PeriodicExportingMetricReader"
+    )
+    @patch("manage_breast_screening.notifications.services.metrics.metrics")
+    @patch("manage_breast_screening.notifications.services.metrics.MeterProvider")
+    def test_metrics_initialisation(
+        self,
+        mock_meter_provider,
+        mock_metrics,
+        mock_metric_reader,
+        mock_metric_exporter,
+        conn_string,
+    ):
+        mock_meter = MagicMock()
+        mock_gauge = MagicMock()
+        mock_metrics.get_meter.return_value = mock_meter
+        mock_meter.create_gauge.return_value = mock_gauge
+
+        subject = Metrics("metric-name", "metric-units", "metric-description")
+
+        mock_metric_exporter.assert_called_once_with(connection_string=str(conn_string))
+        mock_metric_reader.assert_called_once_with(mock_metric_exporter.return_value)
+        mock_meter_provider.assert_called_once_with(
+            metric_readers=[mock_metric_reader.return_value]
+        )
+        mock_metrics.set_meter_provider.assert_called_once_with(
+            mock_meter_provider.return_value
         )
+        mock_metrics.get_meter.assert_called_once_with(
+            "manage_breast_screening.notifications.services.metrics"
+        )
+        mock_meter.create_gauge.assert_called_once_with(
+            "metric-name", unit="metric-units", description="metric-description"
+        )
+        assert subject.gauge == mock_gauge
 
-    @pytest.fixture
-    def test_mock_azure_monitor_metric_exporter(self):
-        with patch(
-            "manage_breast_screening.notifications.services.metrics.AzureMonitorMetricExporter"
-        ) as metric:
-            Metrics()
-            metric.assert_called_once()
+    @patch(
+        "manage_breast_screening.notifications.services.metrics.AzureMonitorMetricExporter"
+    )
+    @patch(
+        "manage_breast_screening.notifications.services.metrics.PeriodicExportingMetricReader"
+    )
+    @patch("manage_breast_screening.notifications.services.metrics.metrics")
+    @patch("manage_breast_screening.notifications.services.metrics.MeterProvider")
+    def test_add(
+        self,
+        mock_meter_provider,
+        mock_metrics,
+        mock_metric_reader,
+        mock_metric_exporter,
+    ):
+        mock_meter = MagicMock()
+        mock_gauge = MagicMock()
+        mock_metrics.get_meter.return_value = mock_meter
+        mock_meter.create_gauge.return_value = mock_gauge
+
+        subject = Metrics("TheQ", "yards", "desc")
+        subject.add("Yay!")
+
+        subject.gauge.set.assert_called_once_with("Yay!", {"queue_name": "TheQ"})