Add a test for exception leakage described in pytest-dev#187

Unfortunately at this moment this is still failing because
of pytest-dev/pytest#2798, we will need to fix this in pytest
first before being able to merge this.

pytestqt/exceptions.py

@@ -1,6 +1,8 @@
-from contextlib import contextmanager
+import functools
 import sys
 import traceback
+from contextlib import contextmanager
+
 import pytest
 
 
@@ -19,6 +21,12 @@ def capture_exceptions():
         manager.finish()
 
 
+def _except_hook(type_, value, tback, exceptions=None):
+    """Hook functions installed by _QtExceptionCaptureManager"""
+    exceptions.append((type_, value, tback))
+    sys.stderr.write(format_captured_exceptions([(type_, value, tback)]))
+
+
 class _QtExceptionCaptureManager(object):
     """
     Manages exception capture context.
@@ -32,12 +40,8 @@ def start(self):
         """Start exception capturing by installing a hook into sys.excepthook
         that records exceptions received into ``self.exceptions``.
         """
-        def hook(type_, value, tback):
-            self.exceptions.append((type_, value, tback))
-            sys.stderr.write(format_captured_exceptions([(type_, value, tback)]))
-
         self.old_hook = sys.excepthook
-        sys.excepthook = hook
+        sys.excepthook = functools.partial(_except_hook, exceptions=self.exceptions)
 
     def finish(self):
         """Stop exception capturing, restoring the original hook.
@@ -60,8 +64,7 @@ def fail_if_exceptions_occurred(self, when):
             prefix = '%s ERROR: ' % when
             msg = prefix + format_captured_exceptions(exceptions)
             del exceptions[:]  # Don't keep exceptions alive longer.
-            pytest.fail(msg,
-                        pytrace=False)
+            pytest.fail(msg, pytrace=False)
 
 
 def format_captured_exceptions(exceptions):

tests/test_exceptions.py

@@ -314,3 +314,37 @@ def event(self, ev):
     del exceptions[:]
     _out, err = capsys.readouterr()
     assert "raise RuntimeError('event processed')" in err
+
+
+def test_exceptions_dont_leak(testdir):
+    """
+    Ensure exceptions are cleared when an exception occurs and don't leak (#187).
+    """
+    testdir.makepyfile("""
+        from pytestqt.qt_compat import qt_api
+        import gc
+        import weakref
+    
+        class MyWidget(qt_api.QWidget):
+    
+            def event(self, ev):
+                called.append(1)
+                raise RuntimeError('event processed')
+                
+        weak_ref = None
+        called = []
+        
+        def test_1(qapp):
+            global weak_ref
+            w = MyWidget()
+            weak_ref = weakref.ref(w)        
+            qapp.postEvent(w, qt_api.QEvent(qt_api.QEvent.User))
+            qapp.processEvents()    
+            
+        def test_2(qapp):
+            assert called     
+            gc.collect()       
+            assert weak_ref() is None
+    """)
+    result = testdir.runpytest()
+    result.stdout.fnmatch_lines(['*1 failed, 1 passed*'])