Add tests for metrics: refactor sampling rate tests and add Prometheus exporter mocks

Author: Borda

tests/test_exporters.py

@@ -464,6 +464,82 @@ def test_func(x):
         test_func.clear_cache()
 
 
+@pytest.mark.memory
+def test_prometheus_collector_collect_mocked():
+    """Test CachierCollector.collect() loop using mocked metric family types.
+
+    Covers lines 81-99 without requiring prometheus_client to be installed.
+
+    """
+    from unittest.mock import MagicMock, patch
+
+    from cachier.exporters.prometheus import CachierCollector
+
+    @cachier(backend="memory", enable_metrics=True)
+    def test_func(x):
+        return x * 2
+
+    test_func.clear_cache()
+    test_func(5)
+    test_func(5)
+
+    exporter = PrometheusExporter(port=0, use_prometheus_client=False)
+    exporter.register_function(test_func)
+
+    with (
+        patch("cachier.exporters.prometheus.CounterMetricFamily", lambda *a, **kw: MagicMock()),
+        patch("cachier.exporters.prometheus.GaugeMetricFamily", lambda *a, **kw: MagicMock()),
+    ):
+        collector = CachierCollector(exporter)
+        results = list(collector.collect())
+        # 5 counter families + 3 gauge families
+        assert len(results) == 8
+
+    test_func.clear_cache()
+
+
+@pytest.mark.memory
+def test_prometheus_start_prometheus_server_mocked():
+    """Test _start_prometheus_server and its MetricsHandler without prometheus_client.
+
+    Covers lines 285-329 (start() prom branch, MetricsHandler.do_GET, log_message).
+
+    """
+    import sys
+    import urllib.request
+    from http.client import HTTPConnection
+    from unittest.mock import MagicMock, patch
+
+    mock_exposition = MagicMock()
+    mock_exposition.generate_latest.return_value = b"# mocked metrics"
+    mock_exposition.CONTENT_TYPE_LATEST = "text/plain"
+
+    prom_mock = MagicMock()
+    prom_mock.exposition = mock_exposition
+
+    exporter = PrometheusExporter(port=0, use_prometheus_client=False)
+    # Manually inject prometheus state to trigger _start_prometheus_server path
+    exporter._prom_client = prom_mock
+    exporter._registry = MagicMock()
+
+    with patch.dict(sys.modules, {"prometheus_client": prom_mock, "prometheus_client.exposition": mock_exposition}):
+        exporter.start()
+        actual_port = exporter._server.server_address[1]
+        assert exporter._server is not None
+        try:
+            response = urllib.request.urlopen(f"http://127.0.0.1:{actual_port}/metrics", timeout=5)
+            assert b"# mocked metrics" in response.read()
+
+            conn = HTTPConnection("127.0.0.1", actual_port)
+            conn.request("GET", "/notfound")
+            resp = conn.getresponse()
+            assert resp.status == 404
+            conn.close()
+        finally:
+            exporter.stop()
+    assert exporter._server is None
+
+
 @pytest.mark.memory
 def test_prometheus_collector_collect_skips_none_metrics():
     """Test CachierCollector.collect() skips functions where metrics is None."""

tests/test_metrics.py

@@ -450,14 +450,20 @@ async def async_func(x):
 
 
 def test_metrics_zero_sampling_rate():
-    """Test that sampling_rate=0.0 records nothing."""
+    """Test that sampling_rate=0.0 records nothing for all record_* methods."""
     metrics = CacheMetrics(sampling_rate=0.0)
-    for _ in range(100):
-        metrics.record_hit()
-        metrics.record_miss()
+    metrics.record_hit()
+    metrics.record_miss()
+    metrics.record_stale_hit()
+    metrics.record_wait_timeout()
+    metrics.record_size_limit_rejection()
+    metrics.record_latency(0.1)
     stats = metrics.get_stats()
-    # With 0.0 rate nothing should be sampled
     assert stats.total_calls == 0
+    assert stats.stale_hits == 0
+    assert stats.wait_timeouts == 0
+    assert stats.size_limit_rejections == 0
+    assert stats.avg_latency_ms == 0.0
 
 
 def test_metrics_get_stats_zero_window():
@@ -490,18 +496,15 @@ def test_metrics_wait_timeout_direct():
     assert stats.wait_timeouts == 1
 
 
-def test_metrics_sampling_rate_zero_skips_all_methods():
-    """Test that sampling_rate=0.0 causes all record_* methods to skip recording."""
-    metrics = CacheMetrics(sampling_rate=0.0)
-    metrics.record_stale_hit()
-    metrics.record_wait_timeout()
-    metrics.record_size_limit_rejection()
-    metrics.record_latency(0.1)
-    stats = metrics.get_stats()
-    assert stats.stale_hits == 0
-    assert stats.wait_timeouts == 0
-    assert stats.size_limit_rejections == 0
-    assert stats.avg_latency_ms == 0.0
+def test_should_sample_deterministic():
+    """Test _should_sample returns True/False deterministically via mocking."""
+    from unittest.mock import patch
+
+    metrics = CacheMetrics(sampling_rate=0.5)
+    with patch.object(metrics._random, "random", return_value=0.1):
+        assert metrics._should_sample() is True
+    with patch.object(metrics._random, "random", return_value=0.9):
+        assert metrics._should_sample() is False
 
 
 def test_metrics_context_manager():