Move garbage collection to session fixture

tests/conftest.py

@@ -1,3 +1,4 @@
+import gc
 import logging
 import os
 import warnings
@@ -18,10 +19,16 @@
 from ipykernel.kernelbase import Kernel
 from ipykernel.zmqshell import ZMQInteractiveShell
 
-# ensure we don't leak History managers
+# ensure we don't leak history managers
 if os.name != "nt":
     HistoryManager._max_inst = 1
 
+
+@pytest.fixture(scope="session", autouse=True)
+def _garbage_collection(request):
+    gc.collect()
+
+
 try:
     import resource
 except ImportError:

tests/test_kernel.py

@@ -4,7 +4,6 @@
 # Distributed under the terms of the Modified BSD License.
 
 import ast
-import gc
 import os.path
 import platform
 import signal
@@ -602,7 +601,6 @@ def test_control_thread_priority():
 
 
 def test_sequential_control_messages():
-    gc.collect()
     with new_kernel() as kc:
         msg_id = kc.execute("import time")
         get_reply(kc, msg_id)

tests/test_kernelapp.py

@@ -1,4 +1,3 @@
-import gc
 import json
 import os
 import threading
@@ -31,7 +30,6 @@ def test_blackhole():
 
 
 def test_start_app():
-    gc.collect()
     app = IPKernelApp()
     app.kernel = MockKernel()