substiture IOError with more appropriate ValueError

tests/integration/test_register_persister.py

@@ -1,5 +1,5 @@
 # -*- coding: utf-8 -*-
-'''Tests for cassettes with overriden persistence'''
+'''Tests for cassettes with custom persistence'''
 
 # External imports
 import os
@@ -11,7 +11,7 @@ from vcr.persisters.filesystem import FilesystemPersister
 
 
 def test_save_cassette_with_custom_persister(tmpdir, httpbin):
-    '''Ensure you can save a cassette using save_callback'''
+    '''Ensure you can save a cassette using custom persister'''
     my_vcr = vcr.VCR()
     my_vcr.register_persister(FilesystemPersister)
 
@@ -28,7 +28,7 @@ def test_save_cassette_with_custom_persister(tmpdir, httpbin):
 
 def test_load_cassette_with_custom_persister(tmpdir, httpbin):
     '''
-    Ensure you can load a cassette using load_callback
+    Ensure you can load a cassette using custom persister
     '''
     my_vcr = vcr.VCR()
     my_vcr.register_persister(FilesystemPersister)

vcr/cassette.py

@@ -288,7 +288,7 @@ class Cassette(object):
                 self.append(request, response)
             self.dirty = False
             self.rewound = True
-        except IOError:
+        except ValueError:
             pass
 
     def __str__(self):

vcr/persisters/filesystem.py

@@ -1,3 +1,5 @@
+# .. _persister_example:
+
 import os
 from ..serialize import serialize, deserialize
 
@@ -6,8 +8,11 @@ class FilesystemPersister(object):
 
     @classmethod
     def load_cassette(cls, cassette_path, serializer):
-        with open(cassette_path) as f:
-            cassette_content = f.read()
+        try:
+            with open(cassette_path) as f:
+                cassette_content = f.read()
+        except IOError:
+            raise ValueError('Cassette not found.')
         cassette = deserialize(cassette_content, serializer)
         return cassette