wcfs: tests: Move tests for crashing WCFS due to old data to dedicated section

Soon this test will also exercise functionality from isolation protocol
as well and so it will stop to be basic.

Move plus rename test_wcfs_basic_invalidation_wo_dFtail_coverage ->
test_wcfs_crash_old_data.

Still crashing in test_wcfs_watch_setup.

wcfs/wcfs_test.py

@@ -1323,29 +1323,6 @@ def test_wcfs_basic_read_aftertail():
     assert _(100*blksize)   == b''
 
 
-# verify that wcfs does not panic with "no current transaction" when processing
-# invalidations if it needs to access ZODB during handleδZ.
-@func
-def test_wcfs_basic_invalidation_wo_dFtail_coverage():
-    # start wcfs with ΔFtail/ΔBtail not covering initial data.
-    t = tDB(old_data=[{0:'a'}]); zf = t.zfile
-    defer(t.close)
-
-    f = t.open(zf)
-    t.commit(zf, {1:'b1'})  # arbitrary commit to non-0 blk
-    f.assertBlk(0, 'a')     # [0] becomes tracked
-
-    # wcfs was crashing on processing further invalidation to blk 0 because
-    # - ΔBtail.GetAt([0], head) returns valueExact=false, and so
-    # - ΔFtail.BlkRevAt activates "access ZODB" codepath,
-    # - but handleδZ was calling ΔFtail.BlkRevAt without properly putting zhead's transaction into ctx.
-    # -> panic.
-    t.commit(zf, {0:'a2'})
-
-    # just in case
-    f.assertBlk(0, 'a2')
-
-
 
 # ---- verify wcfs functionality that depends on isolation protocol ----
 
@@ -1843,6 +1820,30 @@ def test_wcfs_watch_2files():
 # TODO new watch request while previous watch request is in progress (over the same /head/watch handle)
 # TODO @revX/ is automatically removed after some time
 
+# ----------------------------------------
+
+# verify that wcfs does not panic with "no current transaction" when processing
+# invalidations if it needs to access ZODB during handleδZ.
+@func
+def test_wcfs_crash_old_data():
+    # start wcfs with ΔFtail/ΔBtail not covering initial data.
+    t = tDB(old_data=[{0:'a'}]); zf = t.zfile
+    defer(t.close)
+
+    f = t.open(zf)
+    t.commit(zf, {1:'b1'})  # arbitrary commit to non-0 blk
+    f.assertBlk(0, 'a')     # [0] becomes tracked
+
+    # wcfs was crashing on processing further invalidation to blk 0 because
+    # - ΔBtail.GetAt([0], head) returns valueExact=false, and so
+    # - ΔFtail.BlkRevAt activates "access ZODB" codepath,
+    # - but handleδZ was calling ΔFtail.BlkRevAt without properly putting zhead's transaction into ctx.
+    # -> panic.
+    t.commit(zf, {0:'a2'})
+
+    # just in case
+    f.assertBlk(0, 'a2')
+
 
 # ---- misc ---