Use scheduler state instead of task state for warning condition and add tests

- Replace `self._active_task is None` with `not self._scheduler._stopped` in warning condition
- Add comprehensive tests to verify warning behavior when scheduler is stopped vs running
- Tests confirm warning is suppressed when scheduler is intentionally stopped (e.g., in task mode)
- Tests confirm warning still appears when scheduler should be running but is delayed

Co-authored-by: benoit-cty <6603048+benoit-cty@users.noreply.github.com>

Author: Copilot

codecarbon/emissions_tracker.py

@@ -843,7 +843,7 @@ def _measure_power_and_energy(self) -> None:
             raise e
 
         warning_duration = self._measure_power_secs * 3
-        if last_duration > warning_duration and self._active_task is None:
+        if last_duration > warning_duration and not self._scheduler._stopped:
             warn_msg = (
                 "Background scheduler didn't run for a long period"
                 + " (%ds), results might be inaccurate"

tests/test_emissions_tracker.py

@@ -520,3 +520,77 @@ def test_carbon_tracker_offline_context_manager(
         self.assertEqual("United States", emissions_df["country_name"].values[0])
         self.assertEqual("USA", emissions_df["country_iso_code"].values[0])
         self.assertIsInstance(tracker.final_emissions, float)
+    
+    @mock.patch("codecarbon.emissions_tracker.logger")
+    def test_scheduler_warning_suppressed_when_stopped(
+        self,
+        mock_logger,
+        mock_setup_intel_cli,
+        mock_log_values,
+        mocked_get_gpu_details,
+        mocked_env_cloud_details,
+        mocked_is_gpu_details_available,
+    ):
+        """Test that scheduler warning is suppressed when scheduler is stopped."""
+        with EmissionsTracker(
+            output_dir=self.temp_path,
+            measure_power_secs=1,  # Short interval for testing
+        ) as tracker:
+            # Stop the scheduler to simulate task mode or manual stopping
+            tracker._scheduler.stop()
+            
+            # Artificially set last measured time to simulate long delay
+            import time
+            tracker._last_measured_time = time.perf_counter() - 10  # 10 seconds ago
+            
+            # Reset mock to clear any previous warning calls
+            mock_logger.warning.reset_mock()
+            
+            # Call _measure_power_and_energy directly - this would normally trigger warning
+            tracker._measure_power_and_energy()
+            
+            # Verify that if warning was called, it wasn't the scheduler warning
+            if mock_logger.warning.called:
+                for call in mock_logger.warning.call_args_list:
+                    args, kwargs = call
+                    if args and "Background scheduler didn't run for a long period" in str(args[0]):
+                        self.fail("Scheduler warning was called when it should have been suppressed")
+    
+    @mock.patch("codecarbon.emissions_tracker.logger")
+    def test_scheduler_warning_shown_when_running(
+        self,
+        mock_logger,
+        mock_setup_intel_cli,
+        mock_log_values,
+        mocked_get_gpu_details,
+        mocked_env_cloud_details,
+        mocked_is_gpu_details_available,
+    ):
+        """Test that scheduler warning is shown when scheduler is running but delayed."""
+        with EmissionsTracker(
+            output_dir=self.temp_path,
+            measure_power_secs=1,  # Short interval for testing
+        ) as tracker:
+            # Ensure scheduler is running (default state)
+            self.assertFalse(tracker._scheduler._stopped)
+            
+            # Artificially set last measured time to simulate long delay
+            import time
+            tracker._last_measured_time = time.perf_counter() - 10  # 10 seconds ago
+            
+            # Reset mock to clear any previous warning calls
+            mock_logger.warning.reset_mock()
+            
+            # Call _measure_power_and_energy directly - this should trigger warning
+            tracker._measure_power_and_energy()
+            
+            # Verify warning was logged since scheduler should be running
+            scheduler_warning_found = False
+            if mock_logger.warning.called:
+                for call in mock_logger.warning.call_args_list:
+                    args, kwargs = call
+                    if args and "Background scheduler didn't run for a long period" in str(args[0]):
+                        scheduler_warning_found = True
+                        break
+            
+            self.assertTrue(scheduler_warning_found, "Expected scheduler warning was not found")