From 191ce078e71d2ffd9672ee8021064934041215c0 Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Thu, 15 Oct 2020 22:11:26 +0530
Subject: [PATCH] plugin_err must always be a string

---
 src/calibre/constants.py  | 2 +-
 src/calibre/test_build.py | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/calibre/constants.py b/src/calibre/constants.py
index 01dcf6a46f..c27511c635 100644
--- a/src/calibre/constants.py
+++ b/src/calibre/constants.py
@@ -316,7 +316,7 @@ class Plugins(collections.Mapping):
     def __getitem__(self, name):
         from importlib import import_module
         try:
-            return import_module('calibre_extensions.' + name), None
+            return import_module('calibre_extensions.' + name), ''
         except ModuleNotFoundError:
             raise KeyError('No plugin named %r'%name)
         except Exception as err:
diff --git a/src/calibre/test_build.py b/src/calibre/test_build.py
index df49f1ad59..de45f0cb66 100644
--- a/src/calibre/test_build.py
+++ b/src/calibre/test_build.py
@@ -114,7 +114,7 @@ class BuildTest(unittest.TestCase):
                     ctypes.CDLL(os.path.join(plugins_loc, name + ('.dylib' if ismacos else '.so')))
                 continue
             mod, err = plugins[name]
-            self.assertFalse(err or not mod, 'Failed to load plugin: ' + name + ' with error:\n' + err)
+            self.assertTrue(mod, f'Failed to load plugin: {name} with error: {err}')
 
     def test_lxml(self):
         from calibre.utils.cleantext import test_clean_xml_chars