Add unit tests for base helper modules (#797)

- add unit tests for base metrics, logging, spec, parameter_spec,
  and flow modules
- add a lightweight test-only module loader so these tests can run
  without optional runtime dependencies
- fix Parameter.start/stop to accept self

tests/unit/test_base/test_metrics.py

@@ -0,0 +1,129 @@
+from unittest.mock import MagicMock
+
+import pytest
+
+from trustgraph.base import metrics
+
+
+@pytest.fixture(autouse=True)
+def reset_metric_singletons():
+    classes_and_attrs = {
+        metrics.ConsumerMetrics: [
+            "state_metric",
+            "request_metric",
+            "processing_metric",
+            "rate_limit_metric",
+        ],
+        metrics.ProducerMetrics: ["producer_metric"],
+        metrics.ProcessorMetrics: ["processor_metric"],
+        metrics.SubscriberMetrics: [
+            "state_metric",
+            "received_metric",
+            "dropped_metric",
+        ],
+    }
+
+    for cls, attrs in classes_and_attrs.items():
+        for attr in attrs:
+            if hasattr(cls, attr):
+                delattr(cls, attr)
+
+    yield
+
+    for cls, attrs in classes_and_attrs.items():
+        for attr in attrs:
+            if hasattr(cls, attr):
+                delattr(cls, attr)
+
+
+def test_consumer_metrics_reuses_singletons_and_records_events(monkeypatch):
+    enum_factory = MagicMock()
+    histogram_factory = MagicMock()
+    counter_factory = MagicMock()
+
+    state_labels = MagicMock()
+    request_labels = MagicMock()
+    processing_labels = MagicMock()
+    rate_limit_labels = MagicMock()
+    timer = MagicMock()
+
+    enum_factory.return_value.labels.return_value = state_labels
+    histogram_factory.return_value.labels.return_value = request_labels
+    request_labels.time.return_value = timer
+    counter_factory.side_effect = [
+        MagicMock(labels=MagicMock(return_value=processing_labels)),
+        MagicMock(labels=MagicMock(return_value=rate_limit_labels)),
+    ]
+
+    monkeypatch.setattr(metrics, "Enum", enum_factory)
+    monkeypatch.setattr(metrics, "Histogram", histogram_factory)
+    monkeypatch.setattr(metrics, "Counter", counter_factory)
+
+    first = metrics.ConsumerMetrics("proc", "flow", "name")
+    second = metrics.ConsumerMetrics("proc-2", "flow-2", "name-2")
+
+    assert enum_factory.call_count == 1
+    assert histogram_factory.call_count == 1
+    assert counter_factory.call_count == 2
+
+    first.process("ok")
+    first.rate_limit()
+    first.state("running")
+    assert first.record_time() is timer
+
+    processing_labels.inc.assert_called_once_with()
+    rate_limit_labels.inc.assert_called_once_with()
+    state_labels.state.assert_called_once_with("running")
+
+
+def test_producer_metrics_increments_counter_once(monkeypatch):
+    counter_factory = MagicMock()
+    labels = MagicMock()
+    counter_factory.return_value.labels.return_value = labels
+    monkeypatch.setattr(metrics, "Counter", counter_factory)
+
+    producer_metrics = metrics.ProducerMetrics("proc", "flow", "output")
+    producer_metrics.inc()
+
+    counter_factory.assert_called_once()
+    labels.inc.assert_called_once_with()
+
+
+def test_processor_metrics_reports_info(monkeypatch):
+    info_factory = MagicMock()
+    labels = MagicMock()
+    info_factory.return_value.labels.return_value = labels
+    monkeypatch.setattr(metrics, "Info", info_factory)
+
+    processor_metrics = metrics.ProcessorMetrics("proc")
+    processor_metrics.info({"kind": "test"})
+
+    info_factory.assert_called_once()
+    labels.info.assert_called_once_with({"kind": "test"})
+
+
+def test_subscriber_metrics_tracks_received_state_and_dropped(monkeypatch):
+    enum_factory = MagicMock()
+    counter_factory = MagicMock()
+
+    state_labels = MagicMock()
+    received_labels = MagicMock()
+    dropped_labels = MagicMock()
+
+    enum_factory.return_value.labels.return_value = state_labels
+    counter_factory.side_effect = [
+        MagicMock(labels=MagicMock(return_value=received_labels)),
+        MagicMock(labels=MagicMock(return_value=dropped_labels)),
+    ]
+
+    monkeypatch.setattr(metrics, "Enum", enum_factory)
+    monkeypatch.setattr(metrics, "Counter", counter_factory)
+
+    subscriber_metrics = metrics.SubscriberMetrics("proc", "flow", "input")
+    subscriber_metrics.received()
+    subscriber_metrics.state("running")
+    subscriber_metrics.dropped("ignored")
+
+    received_labels.inc.assert_called_once_with()
+    dropped_labels.inc.assert_called_once_with()
+    state_labels.state.assert_called_once_with("running")