Avoid duplicating prefix when re-using urls

If a reponse includes an absolute link, re-using that link as the
url in a subsequent test when a prefix is being used in the tests
can result in a 404 because the prefix will be duplicated.

This change ensures that the prefix will not be duplicated if the
URL already begins with the prefix.

Fixes #165

gabbi/tests/gabbits_intercept/prefix.yaml

@@ -0,0 +1,16 @@
+
+tests:
+
+- name: provide a link in response
+  POST: /
+  request_headers:
+      content-type: application/json
+  data:
+      link: $ENVIRON['GABBI_PREFIX']/barnabas
+
+- name: get that link
+  GET: $RESPONSE['$.link']
+  response_headers: 
+      x-gabbi-url: "///[a-f0-9:-]+$ENVIRON['GABBI_PREFIX']/barnabas/"
+
+

gabbi/utils.py

@@ -53,7 +53,8 @@ def create_url(base_url, host, port=None, prefix='', ssl=False):
     path = parsed_url.path
 
     # Guard against a prefix of None
-    if prefix:
+    # Without the startswith check, the tests in prefix.yaml fail.
+    if prefix and not path.startswith(prefix):
         path = '%s%s' % (prefix, path)
 
     return urlparse.urlunsplit((scheme, netloc, path, query_string, ''))

tox.ini

@@ -8,6 +8,7 @@ deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
 install_command = pip install -U {opts} {packages}
 commands = python setup.py testr --testr-args="{posargs}"
+setenv = GABBI_PREFIX=
 passenv = GABBI_* HOME
 
 [testenv:venv]