diff --git a/Lib/idlelib/run.py b/Lib/idlelib/run.py
index 53e80a9b428..8974b52674f 100644
--- a/Lib/idlelib/run.py
+++ b/Lib/idlelib/run.py
@@ -91,13 +91,20 @@ def capture_warnings(capture):
             _warnings_showwarning = None
 
 capture_warnings(True)
-tcl = tkinter.Tcl()
 
-def handle_tk_events(tcl=tcl):
-    """Process any tk events that are ready to be dispatched if tkinter
-    has been imported, a tcl interpreter has been created and tk has been
-    loaded."""
-    tcl.eval("update")
+if idlelib.testing:
+    # gh-121008: When testing IDLE, don't create a Tk object to avoid side
+    # effects such as installing a PyOS_InputHook hook.
+    def handle_tk_events():
+        pass
+else:
+    tcl = tkinter.Tcl()
+
+    def handle_tk_events(tcl=tcl):
+        """Process any tk events that are ready to be dispatched if tkinter
+        has been imported, a tcl interpreter has been created and tk has been
+        loaded."""
+        tcl.eval("update")
 
 # Thread shared globals: Establish a queue between a subthread (which handles
 # the socket) and the main thread (which runs user code), plus global