test: try adding coverage for QThread

pyproject.toml

@@ -240,7 +240,7 @@ exclude_also = [
     "if __name__ == __main__:",
     "except varname.VarnameRetrievingError:",
     "if TYPE_CHECKING:",
-    "QtCore.QThread",
+    # "QtCore.QThread",
 ]
 
 [tool.mypy]

src/erlab/interactive/imagetool/manager.py

@@ -50,6 +50,9 @@ def __init__(self):
         self.stopped = threading.Event()
 
     def run(self):
+        if threading._trace_hook:
+            sys.settrace(threading._trace_hook)  # For test coverage
+
         self.stopped.clear()
         soc = socket.socket()
         soc.bind(("127.0.0.1", PORT))