nti.fakestatsd

nti.fakestatsd is a testing client for verifying StatsD metrics emitted by perfmetrics.

It’s easy to create a new client for use in testing:

>>> from nti.fakestatsd import FakeStatsDClient
>>> test_client = FakeStatsDClient()

This client exposes the same public interface as perfmetrics.statsd.StatsdClient. For example we can increment counters, set gauges, etc:

>>> test_client.incr('request_c')
>>> test_client.gauge('active_sessions', 320)

Unlike perfmetrics.statsd.StatsdClient, ~.FakeStatsDClient simply tracks the statsd packets that would be sent. This information is exposed on our test_client both as the raw statsd packet, and for convenience this information is also parsed and exposed as ~.Metric objects. For complete details see ~.FakeStatsDClient and ~.Metric.

>>> test_client.packets
['request_c:1|c', 'active_sessions:320|g']
>>> test_client.metrics
[Observation(name='request_c', value='1', kind='c', sampling_rate=None), Observation(name='active_sessions', value='320', kind='g', sampling_rate=None)]

For validating metrics we provide a set of hamcrest matchers for use in test assertions:

>>> from hamcrest import assert_that
>>> from hamcrest import contains
>>> from nti.fakestatsd.matchers import is_metric
>>> from nti.fakestatsd.matchers import is_gauge

We can use both strings and numbers (or any matcher) for the value:

>>> assert_that(test_client,
...     contains(is_metric('c', 'request_c', '1'),
...              is_gauge('active_sessions', 320)))
>>> assert_that(test_client,
...     contains(is_metric('c', 'request_c', '1'),
...              is_gauge('active_sessions', '320')))
>>> from hamcrest import is_
>>> assert_that(test_client,
...     contains(is_metric('c', 'request_c', '1'),
...              is_gauge('active_sessions', is_('320'))))

If the matching fails, we get a descriptive error:

>>> assert_that(test_client,
...     contains(is_gauge('request_c', '1'),
...              is_gauge('active_sessions', '320')))
Traceback (most recent call last):
...
AssertionError:
Expected: a sequence containing [(an instance of Metric and (an object with a property 'kind' matching 'g' and an object with a property 'name' matching 'request_c' and an object with a property 'value' matching '1')), (an instance of Metric and (an object with a property 'kind' matching 'g' and an object with a property 'name' matching 'active_sessions' and an object with a property 'value' matching '320'))]
       but: item 0: was Metric(name='request_c', value='1', kind='c', sampling_rate=None)

For complete details and the changelog, see the documentation.

Changes