Add a 'plugin tweak' test_eight_code which if set to True will cause calibre to use code intended for the 0.8.x series. Note that this code is in heavy development so only set this tweak if you are OK with having parts of calibre broken.

src/calibre/customize/builtins.py

@@ -10,6 +10,7 @@ from calibre.constants import numeric_version
 from calibre.ebooks.metadata.archive import ArchiveExtract, get_cbz_metadata
 from calibre.ebooks.metadata.opf2 import metadata_to_opf
 from calibre.ebooks.oeb.base import OEB_IMAGES
+from calibre.utils.config import test_eight_code
 
 # To archive plugins {{{
 class HTML2ZIP(FileTypePlugin):
@@ -612,20 +613,25 @@ from calibre.devices.folder_device.driver import FOLDER_DEVICE_FOR_CONFIG
 from calibre.devices.kobo.driver import KOBO
 from calibre.devices.bambook.driver import BAMBOOK
 
-from calibre.ebooks.metadata.fetch import GoogleBooks, ISBNDB, Amazon, \
-    KentDistrictLibrary
-from calibre.ebooks.metadata.douban import DoubanBooks
-from calibre.ebooks.metadata.nicebooks import NiceBooks, NiceBooksCovers
-from calibre.ebooks.metadata.covers import OpenLibraryCovers, \
-        AmazonCovers, DoubanCovers
 from calibre.library.catalog import CSV_XML, EPUB_MOBI, BIBTEX
 from calibre.ebooks.epub.fix.unmanifested import Unmanifested
 from calibre.ebooks.epub.fix.epubcheck import Epubcheck
 
-plugins = [HTML2ZIP, PML2PMLZ, TXT2TXTZ, ArchiveExtract, GoogleBooks, ISBNDB, Amazon,
-        KentDistrictLibrary, DoubanBooks, NiceBooks, CSV_XML, EPUB_MOBI, BIBTEX, Unmanifested,
-        Epubcheck, OpenLibraryCovers, AmazonCovers, DoubanCovers,
-        NiceBooksCovers]
+plugins = [HTML2ZIP, PML2PMLZ, TXT2TXTZ, ArchiveExtract, CSV_XML, EPUB_MOBI, BIBTEX, Unmanifested,
+        Epubcheck, ]
+
+if not test_eight_code:
+    from calibre.ebooks.metadata.fetch import GoogleBooks, ISBNDB, Amazon, \
+        KentDistrictLibrary
+    from calibre.ebooks.metadata.douban import DoubanBooks
+    from calibre.ebooks.metadata.nicebooks import NiceBooks, NiceBooksCovers
+    from calibre.ebooks.metadata.covers import OpenLibraryCovers, \
+            AmazonCovers, DoubanCovers
+
+    plugins += [GoogleBooks, ISBNDB, Amazon,
+        OpenLibraryCovers, AmazonCovers, DoubanCovers,
+        NiceBooksCovers, KentDistrictLibrary, DoubanBooks, NiceBooks]
+
 plugins += [
     ComicInput,
     EPUBInput,

src/calibre/utils/config.py

@@ -784,6 +784,7 @@ def write_tweaks(raw):
 
 
 tweaks = read_tweaks()
+test_eight_code = tweaks.get('test_eight_code', False)
 
 def migrate():
     if hasattr(os, 'geteuid') and os.geteuid() == 0: