The tests verify that there is no concurrency bugs around load,
Connection.open and invalidations. See e.g.

https://github.com/zopefoundation/ZODB/issues/290
https://github.com/zopefoundation/ZEO/issues/155

By including the tests into wendelin.core, we will have CI coverage for
all supported storages (FileStorage, ZEO, NEO), and for all supported
ZODB (currently ZODB4, ZODB4-wc2 and ZODB5).

ZEO5 is know to currently fail zloadrace.
However, even though ZODB#290 was fixed, ZEO5 turned out to also fail on zopenrace:

        def test_zodb_zopenrace():
            # exercises ZODB.Connection + particular storage implementation
    >       zopenrace.main()

    lib/tests/test_zodb.py:382:
    _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
    <decorator-gen-1>:2: in main
        ???
    ../../tools/go/pygolang/golang/__init__.py:103: in _
        return f(*argv, **kw)
    lib/tests/testprog/zopenrace.py:115: in main
        test(zstor)
    <decorator-gen-2>:2: in test
        ???
    ../../tools/go/pygolang/golang/__init__.py:103: in _
        return f(*argv, **kw)
    lib/tests/testprog/zopenrace.py:201: in test
        wg.wait()
    golang/_sync.pyx:246: in golang._sync.PyWorkGroup.wait
        ???
    golang/_sync.pyx:226: in golang._sync.PyWorkGroup.go.pyrunf
        ???
    lib/tests/testprog/zopenrace.py:165: in T1
        t1()
    _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

        def t1():
            transaction.begin()
            zconn = db.open()

            root = zconn.root()
            obj1 = root['obj1']
            obj2 = root['obj2']

            # obj1 - reload it from zstor
            # obj2 - get it from zconn cache
            obj1._p_invalidate()

            # both objects must have the same values
            i1 = obj1.i
            i2 = obj2.i
            if i1 != i2:
    >           raise AssertionError("T1: obj1.i (%d)  !=  obj2.i (%d)" % (i1, i2))
    E           AssertionError: T1: obj1.i (3)  !=  obj2.i (2)

    lib/tests/testprog/zopenrace.py:156: AssertionError