substiture IOError with more appropriate ValueError

tests/integration/test_register_persister.py

@@ -0,0 +1,40 @@
+# -*- coding: utf-8 -*-
+'''Tests for cassettes with custom persistence'''
+
+# External imports
+import os
+from six.moves.urllib.request import urlopen
+
+# Internal imports
+import vcr
+from vcr.persisters.filesystem import FilesystemPersister
+
+
+def test_save_cassette_with_custom_persister(tmpdir, httpbin):
+    '''Ensure you can save a cassette using custom persister'''
+    my_vcr = vcr.VCR()
+    my_vcr.register_persister(FilesystemPersister)
+
+    # Check to make sure directory doesnt exist
+    assert not os.path.exists(str(tmpdir.join('nonexistent')))
+
+    # Run VCR to create dir and cassette file using new save_cassette callback
+    with my_vcr.use_cassette(str(tmpdir.join('nonexistent', 'cassette.yml'))):
+        urlopen(httpbin.url).read()
+
+    # Callback should have made the file and the directory
+    assert os.path.exists(str(tmpdir.join('nonexistent', 'cassette.yml')))
+
+
+def test_load_cassette_with_custom_persister(tmpdir, httpbin):
+    '''
+    Ensure you can load a cassette using custom persister
+    '''
+    my_vcr = vcr.VCR()
+    my_vcr.register_persister(FilesystemPersister)
+
+    test_fixture = str(tmpdir.join('synopsis.json'))
+
+    with my_vcr.use_cassette(test_fixture, serializer='json'):
+        response = urlopen(httpbin.url).read()
+        assert b'difficult sometimes' in response