Make the 'Cannot open version.txt' case testable.

lib/python/App/tests/test_version_txt.py

@@ -31,6 +31,7 @@ class VersionTextTestCase(unittest.TestCase):
 
     def _resetModuleGlobals(self):
         from App import version_txt
+        version_txt._filename = 'version.txt'
         version_txt._version_file = None
         version_txt._version_string = None
         version_txt._zope_version = None
@@ -45,7 +46,9 @@ class VersionTextTestCase(unittest.TestCase):
         os.close(f)
 
     def test_without_version_txt(self):
+        from App import version_txt
         from App.version_txt import getZopeVersion
+        version_txt._filename = ''
         self.assertEqual(getZopeVersion(), (-1, -1, -1, '', -1))
 
     def test_with_version_txt_final(self):

lib/python/App/version_txt.py

@@ -17,16 +17,19 @@ $id$
 import os
 import re
 import sys
+import Zope2
+
+_location = os.path.dirname(Zope2.__file__)
+_filename = 'version.txt'
 
 _version_file = None
 _version_string = None
 _zope_version = None
 
 def _get_filename():
-    import Zope2
     if _version_file is not None:
         return _version_file
-    return os.path.join(os.path.dirname(Zope2.__file__), 'version.txt')
+    return os.path.join(_location, _filename)
 
 def _prep_version_data():
     global _version_string, _zope_version