DM-47764: App metrics unit testing helpers

Add a `MockEventManager` that creates `MockPublishers` which are no-op
publishers that record all published payloads. This is returned from the
config factory function when `enabled` is `False` and a new config key,
`mock`, is `True`.

Payloads are recorded to a list with mixed-in assertion helpers.

changelog.d/20241205_130111_danfuchs_metrics_events_unittest_support.md

@@ -0,0 +1,3 @@
+### New features
+
+- Unit testing helpers for application metrics

docs/documenteer.toml

@@ -53,6 +53,7 @@ nitpick_ignore = [
     ["py:obj", "safir.database._pagination.E"],
     ["py:obj", "safir.redis._storage.S"],
     ["py:obj", "safir.metrics._event_manager.P"],
+    ["py:obj", "safir.metrics._testing.P"],
     # SQLAlchemy DeclarativeBase documentation has references that Sphinx
     # can't resolve properly.
     ["py:class", "sqlalchemy.inspection.Inspectable"],

docs/user-guide/metrics/index.rst

@@ -58,6 +58,7 @@ The Kafka and schema manager values come from the Sasquatch configuration that y
 .. code-block:: shell
 
    METRICS_APPLICATION=myapp
+   METRICS_EVENTS_TOPIC_PREFIX=what.ever
    KAFKA_SECURITY_PROTOCOL=SSL
    KAFKA_BOOSTRAP_SERVERS=sasquatch.kafka-1:9092,sasquatcy.kafka2-9092
    KAFKA_CLUSTER_CA_PATH=/some/path/ca.crt
@@ -232,6 +233,181 @@ But the principle remains the same:
 .. _RequestContext: https://sqr-072.lsst.io/#request-context
 .. _Service: https://sqr-072.lsst.io/#services
 
+
+Unit testing
+============
+
+Setting ``enabled`` to ``False`` and ``mock`` to ``True`` in your metrics configuration will give you a `safir.metrics.MockEventManager`.
+This is a no-op event manager that produces publishers that record all of the events that they publish.
+You can make assertions about these published events in your unit tests.
+
+.. warning::
+
+   Do not use the `safir.metrics.MockEventManager` in any deployed instance of your application.
+   Recorded events are never cleaned up, and memory usage will grow unbounded.
+
+.. code-block:: shell
+
+   METRICS_APPLICATION=myapp
+   METRICS_ENABLED=false
+   METRICS_MOCK=true
+   METRICS_EVENTS_TOPIC_PREFIX=what.ever
+
+.. code-block:: python
+
+   from safir.metrics import metrics_configuration_factory
+
+
+   config = metrics_configuration_factory()
+   manager = config.make_manager()
+
+
+   class SomeEvent(EventPayload):
+       model_config = ConfigDict(ser_json_timedelta="float")
+
+       foo: str
+       count: int
+       duration: float | None
+
+
+   await manager.initialize()
+   pub = await manager.create_publisher("someevent", SomeEvent)
+
+   await pub.publish(SomeEvent(foo="foo1", count=1, duration=1.234))
+   await pub.publish(SomeEvent(foo="foo2", count=2, duration=2.345))
+   await pub.publish(SomeEvent(foo="foo3", count=3, duration=3.456))
+   await pub.publish(SomeEvent(foo="foo4", count=4, duration=None))
+   await pub.publish(SomeEvent(foo="foo5", count=5, duration=5.678))
+
+   await manager.aclose()
+
+   published = pub.published
+
+A mock publisher has an `safir.metrics.MockEventPublisher.published` attribute which is a `safir.metrics.PublishedList` containing of all of the `safir.metrics.EventPayload`'s published by that publisher.
+A `safir.metrics.PublishedList` is a regular Python list with some mixed-in assertion methods.
+All of these assertion methods take a list of dicts and compare them to the ``model_dump(mode="json")`` serialization of the published ``EventPayloads``.
+
+``assert_published``
+--------------------
+
+Use `safir.metrics.PublishedList.assert_published` to assert that some set of payloads is an ordered subset of all of the payloads that were published, with no events in between.
+If not, an exception (a subclass of `AssertionError`) will be raised.
+Other events could have been published before or after the expected payloads.
+
+.. code-block:: python
+
+   pub.assert_published(
+       [
+           {"foo": "foo1", "count": 1, "duration": 1.234},
+           {"foo": "foo2", "count": 2, "duration": 2.345},
+           {"foo": "foo3", "count": 3, "duration": 3.456},
+       ]
+   )
+
+You can also assert that the all of the expected payloads were published in any order, and possibly with events in between:
+
+.. code-block:: python
+
+   pub.assert_published(
+       [
+           {"foo": "foo1", "count": 1, "duration": 1.234},
+           {"foo": "foo3", "count": 3, "duration": 3.456},
+           {"foo": "foo2", "count": 2, "duration": 2.345},
+       ],
+       any_order=True,
+   )
+
+``assert_published_all``
+------------------------
+
+Use `safir.metrics.PublishedList.assert_published_all` to assert that the expected payloads, and only the expected payloads, were published:
+
+.. code-block:: python
+
+   pub.assert_published_all(
+       [
+           {"foo": "foo1", "count": 1, "duration": 1.234},
+           {"foo": "foo2", "count": 2, "duration": 2.345},
+           {"foo": "foo3", "count": 3, "duration": 3.456},
+           {"foo": "foo4", "count": 4, "duration": None},
+           {"foo": "foo5", "count": 5, "duration": 5.678},
+       ],
+   )
+
+This would raise an exception because it is missing the ``foo5`` event:
+
+.. code-block:: python
+
+   pub.assert_published_all(
+       [
+           {"foo": "foo1", "count": 1, "duration": 1.234},
+           {"foo": "foo2", "count": 2, "duration": 2.345},
+           {"foo": "foo3", "count": 3, "duration": 3.456},
+           {"foo": "foo4", "count": 4, "duration": None},
+       ],
+   )
+
+You can use ``any_order`` here too:
+
+.. code-block:: python
+
+   pub.assert_published_all(
+       [
+           {"foo": "foo2", "count": 2, "duration": 2.345},
+           {"foo": "foo5", "count": 5, "duration": 5.678},
+           {"foo": "foo3", "count": 3, "duration": 3.456},
+           {"foo": "foo1", "count": 1, "duration": 1.234},
+           {"foo": "foo4", "count": 4, "duration": None},
+       ],
+       any_order=True,
+   )
+
+``ANY`` and ``NOT_NONE``
+------------------------
+
+You can use `safir.metrics.ANY` to indicate that any value, event `None` is OK.
+This is just a re-export of `unittest.mock.ANY`.
+
+.. code-block:: python
+
+   from safir.metrics import ANY
+
+
+   pub.assert_published_all(
+       [
+           {"foo": "foo3", "count": 3, "duration": ANY},
+           {"foo": "foo4", "count": 4, "duration": ANY},
+       ],
+   )
+
+You can use `safir.metrics.NOT_NONE` to indicate that any value except `None` is OK:
+
+.. code-block:: python
+
+   from safir.metrics import ANY
+
+
+   pub.assert_published_all(
+       [
+           {"foo": "foo3", "count": 3, "duration": NOT_NONE},
+           {"foo": "foo4", "count": 4, "duration": ANY},
+       ],
+   )
+
+This would raise an exception, because ``duration`` for the ``foo4`` payload is `None`:
+
+.. code-block:: python
+
+   from safir.metrics import ANY
+
+
+   pub.assert_published_all(
+       [
+           {"foo": "foo3", "count": 3, "duration": NOT_NONE},
+           {"foo": "foo4", "count": 4, "duration": NOT_NONE},
+       ],
+   )
+
 .. _configuration-details:
 
 Configuration details

safir/src/safir/metrics/__init__.py

@@ -4,13 +4,16 @@
     EventsConfiguration,
     KafkaMetricsConfiguration,
     MetricsConfiguration,
+    MockMetricsConfiguration,
     metrics_configuration_factory,
 )
 from ._event_manager import (
     EventManager,
     EventPublisher,
     KafkaEventManager,
     KafkaEventPublisher,
+    MockEventManager,
+    MockEventPublisher,
     NoopEventManager,
     NoopEventPublisher,
 )
@@ -20,8 +23,21 @@
     KafkaTopicError,
 )
 from ._models import EventMetadata, EventPayload
+from ._testing import (
+    ANY,
+    NOT_NONE,
+    BaseAssertionError,
+    NotPublishedConsecutivelyError,
+    NotPublishedError,
+    PublishedCountError,
+    PublishedList,
+    PublishedTooFewError,
+)
 
 __all__ = [
+    "ANY",
+    "NOT_NONE",
+    "BaseAssertionError",
     "BaseMetricsConfiguration",
     "DisabledMetricsConfiguration",
     "DuplicateEventError",
@@ -37,7 +53,15 @@
     "KafkaTopicError",
     "KafkaTopicError",
     "MetricsConfiguration",
+    "MockEventManager",
+    "MockEventPublisher",
+    "MockMetricsConfiguration",
     "NoopEventManager",
     "NoopEventPublisher",
+    "NotPublishedConsecutivelyError",
+    "NotPublishedError",
+    "PublishedCountError",
+    "PublishedList",
+    "PublishedTooFewError",
     "metrics_configuration_factory",
 ]

safir/src/safir/metrics/_config.py

@@ -15,14 +15,20 @@
 
 from ..kafka import KafkaConnectionSettings, SchemaManagerSettings
 from ._constants import ADMIN_CLIENT_PREFIX, BROKER_PREFIX
-from ._event_manager import EventManager, KafkaEventManager, NoopEventManager
+from ._event_manager import (
+    EventManager,
+    KafkaEventManager,
+    MockEventManager,
+    NoopEventManager,
+)
 
 __all__ = [
     "BaseMetricsConfiguration",
     "DisabledMetricsConfiguration",
     "EventsConfiguration",
     "KafkaMetricsConfiguration",
     "MetricsConfiguration",
+    "MockMetricsConfiguration",
     "metrics_configuration_factory",
 ]
 
@@ -131,6 +137,45 @@ def make_manager(
         )
 
 
+class MockMetricsConfiguration(BaseMetricsConfiguration):
+    """Metrics configuration when metrics publishing is mocked."""
+
+    enabled: Annotated[
+        bool, AfterValidator(lambda x: _require_bool(x, False))
+    ] = Field(
+        ...,
+        title="Whether to send events",
+        description=(
+            "If set to false, no events will be sent and all calls to publish"
+            " events will be no-ops."
+        ),
+        validation_alias=AliasChoices("enabled", "METRICS_ENABLED"),
+    )
+
+    mock: Annotated[bool, AfterValidator(lambda x: _require_bool(x, True))] = (
+        Field(
+            title="Mock publishers",
+            description=(
+                "If set to true, all event publishers will be"
+                " unittest.mock.MagicMock instances which will record all"
+                " calls to their publish methods."
+            ),
+            validation_alias=AliasChoices("mock", "METRICS_MOCK"),
+        )
+    )
+
+    model_config = SettingsConfigDict(extra="ignore", populate_by_name=True)
+
+    def make_manager(
+        self, logger: BoundLogger | None = None
+    ) -> MockEventManager:
+        if not logger:
+            logger = structlog.get_logger("safir.metrics")
+        return MockEventManager(
+            self.application, self.events.topic_prefix, logger
+        )
+
+
 class KafkaMetricsConfiguration(BaseMetricsConfiguration):
     """Metrics configuration when enabled, including Kafka configuration."""
 
@@ -204,7 +249,9 @@ def make_manager(
 
 
 MetricsConfiguration: TypeAlias = (
-    DisabledMetricsConfiguration | KafkaMetricsConfiguration
+    MockMetricsConfiguration
+    | DisabledMetricsConfiguration
+    | KafkaMetricsConfiguration
 )
 """Type to use for metrics configuration in the application config.
 
@@ -262,6 +309,9 @@ class Config(BaseSettings):
     # environment variable settings to enable, and then finally
     # unconditionally try to return the default.
     try:
-        return DisabledMetricsConfiguration()
+        return MockMetricsConfiguration()
     except ValidationError:
-        return KafkaMetricsConfiguration()
+        try:
+            return DisabledMetricsConfiguration()
+        except ValidationError:
+            return KafkaMetricsConfiguration()