get test_ref_cycles to pass (#1539)

* get test_ref_cycles to pass

let objects die without gc.collect()
if you don't have cyclic references, there should be no need to call
gc.collect()

the usage of gc.collect() was causing pytest running with coverage to
crash on Python 3.7 / PySide2 5.12 / {Linux, Windows}.

* remove imports used only by the removed code

pyqtgraph/graphicsItems/tests/test_GraphicsItem.py

@@ -1,4 +1,3 @@
-import gc
 import weakref
 try:
     import faulthandler
@@ -16,7 +15,6 @@ def test_getViewWidget():
     view.addItem(item)
     assert item.getViewWidget() is view
     del view
-    gc.collect()
     assert vref() is None
     assert item.getViewWidget() is None
 
@@ -30,7 +28,6 @@ def test_getViewWidget_deleted():
     obj = pg.QtGui.QWidget()
     view.setParent(obj)
     del obj
-    gc.collect()
 
     assert not pg.Qt.isQObjectAlive(view)
     assert item.getViewWidget() is None

pyqtgraph/tests/test_ref_cycles.py

@@ -5,12 +5,9 @@ Test for unwanted reference cycles
 """
 import pyqtgraph as pg
 import numpy as np
-import gc, weakref
-import pytest
+import weakref
 app = pg.mkQApp()
 
-skipreason = ('This test is failing on pyside and pyside2 for an unknown reason.')
-                 
 def assert_alldead(refs):
     for ref in refs:
         assert ref() is None
@@ -37,7 +34,6 @@ def mkrefs(*objs):
     return [weakref.ref(obj) for obj in allObjs.values()]
 
 
-@pytest.mark.skipif(pg.Qt.QT_LIB in {'PySide'}, reason=skipreason)
 def test_PlotWidget():
     def mkobjs(*args, **kwds):
         w = pg.PlotWidget(*args, **kwds)
@@ -55,7 +51,6 @@ def test_PlotWidget():
     for i in range(5):
         assert_alldead(mkobjs())
     
-@pytest.mark.skipif(pg.Qt.QT_LIB in {'PySide', 'PySide2', 'PySide6'}, reason=skipreason)
 def test_ImageView():
     def mkobjs():
         iv = pg.ImageView()
@@ -63,12 +58,11 @@ def test_ImageView():
         iv.setImage(data)
         
         return mkrefs(iv, iv.imageItem, iv.view, iv.ui.histogram, data)
+
     for i in range(5):
-        gc.collect()
         assert_alldead(mkobjs())
 
 
-@pytest.mark.skipif(pg.Qt.QT_LIB in {'PySide'}, reason=skipreason)
 def test_GraphicsWindow():
     def mkobjs():
         w = pg.GraphicsWindow()

pyqtgraph/widgets/GraphicsView.py

@@ -8,7 +8,6 @@ Distributed under MIT/X11 license. See license.txt for more information.
 from ..Qt import QtCore, QtGui, QtWidgets, QT_LIB
 from ..Point import Point
 import sys, os
-import warnings
 from .FileDialog import FileDialog
 from ..GraphicsScene import GraphicsScene
 import numpy as np
@@ -407,18 +406,3 @@ class GraphicsView(QtGui.QGraphicsView):
         
     def dragEnterEvent(self, ev):
         ev.ignore()  ## not sure why, but for some reason this class likes to consume drag events
-
-    def _del(self):
-        try:
-            if self.parentWidget() is None and self.isVisible():
-                msg = "Visible window deleted. To prevent this, store a reference to the window object."
-                try:
-                    warnings.warn(msg, RuntimeWarning, stacklevel=2)
-                except TypeError:
-                    # warnings module not available during interpreter shutdown
-                    pass
-        except RuntimeError:
-            pass
-
-if sys.version_info[0] == 3 and sys.version_info[1] >= 4:
-    GraphicsView.__del__ = GraphicsView._del