test-filecache.py: make setbeforeget test clearer

'0' and 'None' as outputs tripped me up. Make the distinction between values
set externally and values computed by calling the decorated function clearer.

tests/test-filecache.py

@@ -21,6 +21,7 b' class fakerepo(object):'
     @filecache('x')
     def cached(self):
         print 'creating'
+        return 'string from function'
 
     def invalidate(self):
         for k in self._filecache:
@@ -103,7 +104,7 b' def test_filecache_synced():'
 
 def setbeforeget(repo):
     os.remove('x')
-    repo.cached = 0
+    repo.cached = 'string set externally'
     repo.invalidate()
     print repo.cached
     repo.invalidate()

tests/test-filecache.py.out

@@ -20,6 +20,6 b' working directory now based on revision '
 
 setbeforeget:
 
-0
+string set externally
 creating
-None
+string from function