Fix test failures due to file locking on windows

src/calibre/db/legacy.py

@@ -64,9 +64,11 @@ class LibraryDatabase(object):
         self.backend.close()
 
     def break_cycles(self):
+        delattr(self.backend, 'field_metadata')
         self.data.cache.backend = None
         self.data.cache = None
-        self.data = self.backend = self.new_api = self.field_metadata = self.prefs = self.listeners = self.refresh_ondevice = None
+        for x in ('data', 'backend', 'new_api', 'listeners',):
+            delattr(self, x)
 
     # Library wide properties {{{
     @property

src/calibre/db/tests/legacy.py

@@ -117,18 +117,24 @@ class LegacyTest(BaseTest):
             '__init__',
         }
 
-        for attr in dir(db):
-            if attr in SKIP_ATTRS:
-                continue
-            if not hasattr(ndb, attr):
-                raise AssertionError('The attribute %s is missing' % attr)
-            obj, nobj  = getattr(db, attr), getattr(ndb, attr)
-            if attr not in SKIP_ARGSPEC:
-                try:
-                    argspec = inspect.getargspec(obj)
-                except TypeError:
-                    pass
-                else:
-                    self.assertEqual(argspec, inspect.getargspec(nobj), 'argspec for %s not the same' % attr)
+        try:
+            for attr in dir(db):
+                if attr in SKIP_ATTRS:
+                    continue
+                if not hasattr(ndb, attr):
+                    raise AssertionError('The attribute %s is missing' % attr)
+                obj, nobj  = getattr(db, attr), getattr(ndb, attr)
+                if attr not in SKIP_ARGSPEC:
+                    try:
+                        argspec = inspect.getargspec(obj)
+                    except TypeError:
+                        pass
+                    else:
+                        self.assertEqual(argspec, inspect.getargspec(nobj), 'argspec for %s not the same' % attr)
+        finally:
+            for db in (ndb, db):
+                db.close()
+                db.break_cycles()
+
     # }}}
 

src/calibre/db/tests/writing.py

@@ -374,6 +374,9 @@ class WritingTest(BaseTest):
             ae(cache.field_for('cover', book_id), 1)
             ae(old.cover(book_id, index_is_id=True), img, 'Cover was not set correctly for book %d' % book_id)
             self.assertTrue(old.has_cover(book_id))
+        old.close()
+        old.break_cycles()
+        del old
     # }}}
 
     def test_set_metadata(self):  # {{{