diff --git a/README.rst b/README.rst
index c214c07..3d87551 100644
--- a/README.rst
+++ b/README.rst
@@ -202,6 +202,9 @@ Alternatively, you can use the ``nose`` command (which has a ton of available op
 .. code-block:: shell
 
     nosetests
+    nosetests tests.olsr
+    nosetests tests.olsr:TestOlsrParser
+    nosetests tests.olsr:TestOlsrParser.test_parse
 
 See test coverage with:
 
diff --git a/netdiff/exceptions.py b/netdiff/exceptions.py
index 5176ac5..4289c38 100644
--- a/netdiff/exceptions.py
+++ b/netdiff/exceptions.py
@@ -1,6 +1,14 @@
-class NetParserException(Exception):
+class NetdiffException(Exception):
     pass
 
 
-class NetJsonException(Exception):
+class NetParserException(NetdiffException):
+    pass
+
+
+class NetParserJsonException(NetdiffException):
+    pass
+
+
+class NetJsonException(NetdiffException):
     pass
diff --git a/netdiff/parsers/base.py b/netdiff/parsers/base.py
index 37612df..c83f544 100644
--- a/netdiff/parsers/base.py
+++ b/netdiff/parsers/base.py
@@ -1,5 +1,6 @@
 import six
 import json
+import os
 import requests
 import telnetlib
 from collections import OrderedDict
@@ -9,7 +10,7 @@
 except ImportError:
     import urllib.parse as urlparse
 
-from ..exceptions import NetParserException, NetJsonException
+from ..exceptions import NetParserException, NetParserJsonException, NetJsonException
 
 
 class BaseParser(object):
@@ -57,7 +58,7 @@ def _to_python(self, data):
         if isinstance(data, six.string_types):
             up = urlparse.urlparse(data)
             # if it looks like a file path
-            if True in [data.startswith('./'), data.startswith('../'), data.startswith('/')]:
+            if os.path.isfile(data):
                 data = open(data).read()
             # if it looks like a HTTP URL
             elif up.scheme in ['http', 'https']:
@@ -75,7 +76,7 @@ def _to_python(self, data):
             try:
                 return json.loads(data)
             except ValueError:
-                raise NetParserException('Could not decode JSON data')
+                raise NetParserJsonException('Could not decode JSON data')
         elif isinstance(data, dict):
             return data
         else:
@@ -101,7 +102,7 @@ def json(self, dict=False, **args):
             raise NetJsonException('protocol cannot be None')
         if self.version is None:
             raise NetJsonException('version cannot be None')
-        if self.metric is None:
+        if self.metric is None and self.protocol != 'static':
             raise NetJsonException('metric cannot be None')
         # prepare lists
         nodes = [{'id': node} for node in graph.nodes()]
diff --git a/netdiff/tests.py b/netdiff/tests.py
index 40ccc71..b374002 100644
--- a/netdiff/tests.py
+++ b/netdiff/tests.py
@@ -9,7 +9,7 @@ class TestCase(unittest.TestCase):
     def _test_expected_links(self, links, expected_links):
         """
         Ensures the contents of links is the same of expected_links,
-        indipendently from the ordering
+        independently from the ordering
         links and expected_links should be list of tuples.
         """
         found = 0
diff --git a/tests/base/tests.py b/tests/base/tests.py
index 77e8462..0533c70 100644
--- a/tests/base/tests.py
+++ b/tests/base/tests.py
@@ -3,7 +3,7 @@
 
 from netdiff import get_version
 from netdiff.parsers.base import BaseParser
-from netdiff.exceptions import NetParserException
+from netdiff.exceptions import NetParserException, NetParserJsonException
 
 
 __all__ = ['TestBaseParser']
@@ -20,7 +20,7 @@ def test_parse_file(self):
         path = '{0}/../static/olsr-2-links.json'.format(dir)
         p = BaseParser(path)
         self.assertIsInstance(p.original_data, dict)
-        with self.assertRaises(IOError):
+        with self.assertRaises(NetParserJsonException):
             BaseParser('../wrong.json')
 
     def test_parse_http(self):
@@ -39,7 +39,7 @@ def test_parse_dict(self):
         self.assertIsInstance(p.original_data, dict)
 
     def test_parse_json_exception(self):
-        with self.assertRaises(NetParserException):
+        with self.assertRaises(NetParserJsonException):
             BaseParser('wrong [] ; .')
 
     def test_parse_exception(self):
diff --git a/tests/olsr/tests.py b/tests/olsr/tests.py
index 221352a..2cfe905 100644
--- a/tests/olsr/tests.py
+++ b/tests/olsr/tests.py
@@ -84,7 +84,7 @@ def test_added_1_link(self):
         old = OlsrParser(links2)
         new = OlsrParser(links3)
         result = diff(old, new)
-        # ensure there are no differences
+        # ensure there are differences
         self.assertEqual(len(result['added']), 1)
         self.assertEqual(len(result['removed']), 0)
         # ensure 1 link added
@@ -98,7 +98,7 @@ def test_removed_1_link(self):
         self.assertTrue(type(result) is dict)
         self.assertTrue(type(result['added']) is list)
         self.assertTrue(type(result['removed']) is list)
-        # ensure there are no differences
+        # ensure there are differences
         self.assertEqual(len(result['added']), 0)
         self.assertEqual(len(result['removed']), 1)
         # ensure 1 link removed
@@ -109,7 +109,7 @@ def test_simple_diff(self):
         old = OlsrParser(links3)
         new = OlsrParser(links5)
         result = diff(old, new)
-        # ensure there are no differences
+        # ensure there are differences
         self.assertEqual(len(result['added']), 3)
         self.assertEqual(len(result['removed']), 1)
         # ensure 3 links added