allmydata.test.web.test_web.Web.test_POST_upload_format (and others) fail on PyPy CI

[exarkun]

Traceback (most recent call last):
testtools.testresult.real._StringException: Traceback (most recent call last):
  File "/tmp/tahoe-lafs.tox/pypy27/site-packages/twisted/internet/defer.py", line 151, in maybeDeferred
    result = f(*args, **kw)
  File "/tmp/tahoe-lafs.tox/pypy27/site-packages/allmydata/test/common.py", line 707, in _modify
    new_data = modifier(old_contents, None, True)
  File "/tmp/tahoe-lafs.tox/pypy27/site-packages/allmydata/dirnode.py", line 180, in modify
    children = self.node._unpack_contents(old_contents)
  File "/tmp/tahoe-lafs.tox/pypy27/site-packages/allmydata/dirnode.py", line 391, in _unpack_contents
    child = self._create_and_validate_node(rw_uri, ro_uri, name)
  File "/tmp/tahoe-lafs.tox/pypy27/site-packages/allmydata/dirnode.py", line 338, in _create_and_validate_node
    name=name)
  File "/tmp/tahoe-lafs.tox/pypy27/site-packages/allmydata/nodemaker.py", line 70, in create_from_cap
    node = self._node_cache[memokey]
  File "/opt/pypy/lib-python/2.7/weakref.py", line 105, in __getitem__
    raise KeyError, key
KeyError: 'MURI:MDMF:s42gpc3eevvgni5e7gyvccxbbi:egnwdhmhwtuc2gvpl6j7m7kqr26qqt2lg5a7ysjflze6r5nvim2q'

[sajith]

Another instance of this failure from a few months back: ​https://app.circleci.com/pipelines/github/sajith/tahoe-lafs/231/workflows/e9e005a5-6121-4da8-8b59-1df4e3e67d44/jobs/3150/tests

[exarkun]

​https://github.com/tahoe-lafs/tahoe-lafs/pull/910

[GitHub <noreply@…>]

In 0e4cf0d/trunk:

Merge pull request #910 from tahoe-lafs/3539.nodemaker-weakrefdict

Fix NodeMaker?'s LBYL use of the WeakValueDictionary?

Fixes: ticket:3539