work around an apparent python2.4/python2.5 bug with subprocess.Popen,

causing jenkins failures.  Apparently "os.environ.popitem(name, None)"
is not the same as::

    try:
        del os.environ[name]
    except KeyError:
        pass

_pytest/monkeypatch.py

@@ -95,7 +95,10 @@ class monkeypatch:
         self._setattr[:] = []
         for dictionary, name, value in self._setitem:
             if value is notset:
-                dictionary.pop(name, None)
+                try:
+                    del dictionary[name]
+                except KeyError:
+                    pass # was already deleted, so we have the desired state
             else:
                 dictionary[name] = value
         self._setitem[:] = []

testing/test_monkeypatch.py

@@ -67,12 +67,20 @@ def test_setitem_deleted_meanwhile():
     monkeypatch.undo()
     assert not d
 
-def test_setenv_deleted_meanwhile():
+@pytest.mark.parametrize("before", [True, False])
+def test_setenv_deleted_meanwhile(before):
+    key = "qwpeoip123"
+    if before:
+        os.environ[key] = "world"
     monkeypatch = MonkeyPatch()
-    monkeypatch.setenv('XYZ123', 'hello')
-    del os.environ['XYZ123']
+    monkeypatch.setenv(key, 'hello')
+    del os.environ[key]
     monkeypatch.undo()
-    assert 'XYZ123' not in os.environ
+    if before:
+        assert os.environ[key] == "world"
+        del os.environ[key]
+    else:
+        assert key not in os.environ
 
 def test_delitem():
     d = {'x': 1}

testing/test_runner.py

@@ -436,8 +436,7 @@ def test_pytest_cmdline_main(testdir):
            py.test.cmdline.main([__file__])
     """)
     import subprocess
-    popen = subprocess.Popen([sys.executable, str(p)],
-        stdout=subprocess.PIPE, env={})
+    popen = subprocess.Popen([sys.executable, str(p)], stdout=subprocess.PIPE)
     s = popen.stdout.read()
     ret = popen.wait()
     assert ret == 0