OpenMetrics test: Add parser to check against spec

src/allmydata/test/test_openmetrics.py

@@ -1,4 +1,5 @@
 import mock
+from prometheus_client.openmetrics import parser
 from twisted.trial import unittest
 from allmydata.web.status import Statistics
 
@@ -8,18 +9,21 @@ class FakeStatsProvider(object):
         return stats
 
 class OpenMetrics(unittest.TestCase):
-    def test_header(self):
+    def test_spec_compliance(self):
+        """
+        Does our output adhere to the OpenMetrics spec?
+        https://github.com/OpenObservability/OpenMetrics/blob/main/specification/OpenMetrics.md
+        """
         req = mock.Mock()
         stats = mock.Mock()
         stats._provider = FakeStatsProvider()
         metrics = Statistics.render_OPENMETRICS(stats, req)
+
+        # "The content type MUST be..."
         req.setHeader.assert_called_with("content-type", "application/openmetrics-text; version=1.0.0; charset=utf-8")
 
-    def test_spec_compliance(self):
-        req = mock.Mock()
-        stats = mock.Mock()
-        stats._provider = FakeStatsProvider()
-        metrics = Statistics.render_OPENMETRICS(stats, req)
-        # TODO test that output adheres to spec
+        # The parser throws if it can't parse.
+        # Wrap in a list() to drain the generator.
+        families = list(parser.text_string_to_metric_families(metrics))
         # TODO add more realistic stats, incl. missing (None) values
 

tox.ini

@@ -52,6 +52,8 @@ deps =
      certifi
      # VCS hooks support
      py36,!coverage: pre-commit
+     # Does our OpenMetrics endpoint adhere to the spec:
+     prometheus-client==0.11.0
 
 # We add usedevelop=False because testing against a true installation gives
 # more useful results.