X wc1: Split out demo for failing cache invalidation into xfail'ing test

See 69c94fbc and 48eb692f for description of the problem.

bigfile/tests/test_filezodb.py

@@ -36,6 +36,7 @@ import weakref
 import gc
 
 from pytest import raises
+import pytest; xfail = pytest.mark.xfail
 from six.moves import range as xrange
 
 
@@ -555,7 +556,7 @@ def test_bigfile_filezodb_vs_conn_migration():
 # ZBlk should properly handle 'invalidate' messages from DB
 # ( NOTE this test is almost dupped at test_zbigarray_vs_cache_invalidation() )
 @func
-def test_bigfile_filezodb_vs_cache_invalidation():
+def _test_bigfile_filezodb_vs_cache_invalidation(_drop_cache):
     root = dbopen()
     conn = root._p_jar
     db   = conn.db()
@@ -609,15 +610,14 @@ def test_bigfile_filezodb_vs_cache_invalidation():
     ram_reclaim_all()
     assert Blk(vma2, 0)[0] == 1
 
-#   """
     # FIXME: this simulates ZODB Connection cache pressure and currently
     # removes ZBlk corresponding to blk #0 from conn2 cache.
     # In turn this leads to conn2 missing that block invalidation on follow-up
     # transaction boundary.
     #
     # See FIXME notes on ZBlkBase._p_invalidate() for detailed description.
-    conn2._cache.minimize()
-#   """
+    #conn2._cache.minimize()
+    _drop_cache(conn2)  # XXX change to just conn2._cache.minimize after issue is fixed
 
     tm2.commit()                # transaction boundary for t2
 
@@ -626,6 +626,12 @@ def test_bigfile_filezodb_vs_cache_invalidation():
 
     del conn2, root2
 
+def test_bigfile_filezodb_vs_cache_invalidation():
+    _test_bigfile_filezodb_vs_cache_invalidation(_drop_cache=lambda conn: None)
+@xfail
+def test_bigfile_filezodb_vs_cache_invalidation_with_cache_pressure():
+    _test_bigfile_filezodb_vs_cache_invalidation(_drop_cache=lambda conn: conn._cache.minimize())
+
 
 # verify that conflicts on ZBlk are handled properly
 # ( NOTE this test is almost dupped at test_zbigarray_vs_conflicts() )