adding urljoin function else will get NotImplemented error

Author: kapilkd13

tests/test_fetch.py

@@ -1,4 +1,5 @@
 import unittest
+import urlparse
 
 import schema_salad.main
 import schema_salad.ref_resolver
@@ -26,6 +27,9 @@ def fetch_text(self, url):  # type: (unicode) -> unicode
                 else:
                     raise RuntimeError("Not foo.cwl")
 
+            def urljoin(self, base_url, url):  # type: (Text, Text) -> Text
+                return urlparse.urljoin(base_url, url)
+
             def check_exists(self, url):  # type: (unicode) -> bool
                 if url == "baz:bar/foo.cwl":
                     return True