InfluxDBMixin: Add test for set_metric_tag.

examples/influxdb.py

@@ -32,6 +32,16 @@ class SimpleHandler(metrics.InfluxDBMixin, web.RequestHandler):
 
     """
 
+    @gen.coroutine
+    def prepare(self):
+        maybe_future = super(SimpleHandler, self).prepare()
+        if gen.is_future(maybe_future):
+            yield maybe_future
+
+        if 'Correlation-ID' in self.request.headers:
+            self.set_metric_tag('correlation_id',
+                                self.request.headers['Correlation-ID'])
+
     @gen.coroutine
     def get(self):
         with self.execution_timer('sleepytime'):

tests.py

@@ -1,6 +1,7 @@
 import logging
 import socket
 import time
+import uuid
 
 from tornado import gen, testing, web
 import mock
@@ -190,3 +191,18 @@ class InfluxDbTests(testing.AsyncHTTPTestCase):
         response = self.fetch('/')
         self.assertEqual(response.code, 204)
         self.assertIs(cfg['db_connection'], conn)
+
+    def test_that_metric_tag_is_tracked(self):
+        cid = str(uuid.uuid4())
+        response = self.fetch('/', headers={'Correlation-ID': cid})
+        self.assertEqual(response.code, 204)
+
+        for key, fields, timestamp in self.influx_messages:
+            if key.startswith('my-service,'):
+                tag_dict = dict(a.split('=') for a in key.split(',')[1:])
+                self.assertEqual(tag_dict['correlation_id'],
+                                 '"{}"'.format(cid))
+                break
+        else:
+            self.fail('Expected to find "request" metric in {!r}'.format(
+                    list(self.application.influx_db['requests'])))