feat: Emit Daemon logs for pytest test run

src/aiida/tools/pytest_fixtures/daemon.py

@@ -2,13 +2,15 @@
 
 from __future__ import annotations
 
+import logging
 import pathlib
 import typing as t
 
 import pytest
 
 if t.TYPE_CHECKING:
     from aiida.engine import Process, ProcessBuilder
+    from aiida.engine.daemon.client import DaemonClient
     from aiida.orm import ProcessNode
 
 
@@ -47,7 +49,7 @@ def test(daemon_client):
 
 
 @pytest.fixture
-def started_daemon_client(daemon_client):
+def started_daemon_client(daemon_client: 'DaemonClient'):
     """Ensure that the daemon is running for the test profile and return the associated client.
 
     Usage::
@@ -60,11 +62,61 @@ def test(started_daemon_client):
         daemon_client.start_daemon()
         assert daemon_client.is_daemon_running
 
+    import threading
+    import time
+
+    from watchdog.events import FileSystemEventHandler
+    from watchdog.observers import Observer
+
+    logger = logging.getLogger('tests.daemon:started_daemon_client')
+
+    logger.debug(f'Daemon log file is located at: {daemon_client.daemon_log_file}')
+
+    # This flag will be used to stop the thread when the fixture is torn down
+    stop_thread = False
+
+    class LogFileEventHandler(FileSystemEventHandler):
+        def __init__(self, filepath):
+            self.filepath = filepath
+            # Keep track of how many bytes have been read so we print only new data
+            self._pos = 0
+
+        def on_modified(self, event):
+            if event.src_path == self.filepath:
+                # The file was modified, read from the last known position
+                with open(self.filepath, 'r') as f:
+                    f.seek(self._pos)
+                    new_output = f.read()
+                    if new_output:
+                        logger.debug(new_output)
+                        self._pos = f.tell()
+
+    def print_log_content(check_interval=0.1):
+        event_handler = LogFileEventHandler(daemon_client.daemon_log_file)
+        observer = Observer()
+        _ = observer.schedule(event_handler, str(pathlib.Path(daemon_client.daemon_log_file)), recursive=False)
+        observer.start()
+
+        try:
+            while not stop_thread:
+                time.sleep(check_interval)
+        finally:
+            observer.stop()
+            observer.join()
+
+    # Start a background thread to continuously print new log lines
+    t = threading.Thread(target=print_log_content, daemon=True)
+    t.start()
+
     yield daemon_client
 
+    # After the test finishes, signal the thread to stop and join it
+    stop_thread = True
+    t.join(timeout=5)
+
 
 @pytest.fixture
-def stopped_daemon_client(daemon_client):
+def stopped_daemon_client(daemon_client: 'DaemonClient'):
     """Ensure that the daemon is not running for the test profile and return the associated client.
 
     Usage::