ci: unit test for srt/observability module (#21002)

test/registered/unit/observability/test_cpu_monitor.py

@@ -1,5 +1,8 @@
+import threading
 import time
 import unittest
+from collections import namedtuple
+from unittest.mock import MagicMock, patch
 
 from sglang.test.ci.ci_register import register_cpu_ci
 
@@ -34,5 +37,64 @@ class TestCpuMonitor(unittest.TestCase):
         self.assertGreater(value, 0)
 
 
+class TestCpuMonitorMocked(unittest.TestCase):
+    """Fast, deterministic tests for start_cpu_monitor_thread using mocks."""
+
+    @patch("prometheus_client.Counter")
+    @patch("sglang.srt.observability.cpu_monitor.psutil.Process")
+    @patch("sglang.srt.observability.cpu_monitor.time.sleep")
+    def test_delta_calculation_over_two_iterations(
+        self, mock_sleep, MockProcess, MockCounter
+    ):
+        """Verify delta=(user_diff+system_diff) and last_times update across iterations."""
+        from sglang.srt.observability.cpu_monitor import start_cpu_monitor_thread
+
+        CpuTimes = namedtuple("CpuTimes", ["user", "system"])
+        mock_process = MockProcess.return_value
+        mock_process.cpu_times.side_effect = [
+            CpuTimes(user=1.0, system=0.5),  # initial (L18)
+            CpuTimes(user=2.5, system=1.0),  # iteration 1 (L22)
+            CpuTimes(user=4.0, system=2.0),  # iteration 2 (L22)
+        ]
+
+        # Allow 2 loop iterations, then stop the thread.
+        # Override threading.excepthook to suppress the pytest warning from
+        # the intentional exception used to terminate the monitor loop.
+        remaining = [2]
+        orig_hook = threading.excepthook
+
+        def controlled_sleep(seconds):
+            if remaining[0] <= 0:
+                raise SystemExit
+            remaining[0] -= 1
+
+        mock_sleep.side_effect = controlled_sleep
+        threading.excepthook = lambda args: None
+
+        mock_labeled = MagicMock()
+        MockCounter.return_value.labels.return_value = mock_labeled
+
+        thread = start_cpu_monitor_thread("my_component", interval=3.0)
+        thread.join(timeout=1.0)
+        threading.excepthook = orig_hook
+
+        # Thread is daemon (L29)
+        self.assertTrue(thread.daemon)
+
+        # Sleep called with correct interval (L21)
+        mock_sleep.assert_called_with(3.0)
+
+        # Counter labeled with component (L26)
+        MockCounter.return_value.labels.assert_called_with(component="my_component")
+
+        # Delta calculation (L23-24) and counter increment (L26)
+        inc_calls = mock_labeled.inc.call_args_list
+        self.assertEqual(len(inc_calls), 2)
+        # Iteration 1: (2.5 - 1.0) + (1.0 - 0.5) = 2.0
+        self.assertAlmostEqual(inc_calls[0].args[0], 2.0)
+        # Iteration 2: (4.0 - 2.5) + (2.0 - 1.0) = 2.5 (proves last_times updated)
+        self.assertAlmostEqual(inc_calls[1].args[0], 2.5)
+
+
 if __name__ == "__main__":
     unittest.main()