Fix test_heartbeat_metric_get_metric_init test case

contrib/opencensus-ext-azure/tests/test_azure_heartbeat_metrics.py

@@ -89,9 +89,13 @@ def test_heartbeat_metric_init(self):
         self.assertFalse(metric.init)
         self.assertEqual(len(metric.properties), 0)
 
-    # TODO @lzchen #981
-    @unittest.skip("Failing because github workflow runs on Azure")
-    def test_heartbeat_metric_get_metric_init(self):
+    @mock.patch(
+        'requests.get',
+        throw(requests.exceptions.ConnectionError)
+    )
+    @mock.patch('os.environ.get')
+    def test_heartbeat_metric_get_metric_init(self, environ_mock):
+        environ_mock.return_value = None
         metric = heartbeat_metrics.HeartbeatMetric()
         self.assertFalse(metric.init)
         metrics = metric.get_metrics()