Wrap the http request to trap WSGIAppError and reraise

To create a strong boundary between the client and the server,
wsgi-intercept wraps exceptions raised in the intercepted app in a
WSGIAppError. In most situations this is a good thing. However if
gabbi is being used to do TDD against a nascent API this behavior
can obscure useful traceback information when there is a
catastrophic and untrapped exception in the server code.

To deal with this the WSGIAppError is caught and the contained
exception is reraised in all its glory to spew into STDERR for
debugging purposes.

gabbi/case.py

@@ -27,7 +27,9 @@ import os
 import re
 import sys
 
+import wsgi_intercept
 import jsonpath_rw
+import six
 from six.moves.urllib import parse as urlparse
 from testtools import testcase
 
@@ -243,14 +245,24 @@ class HTTPTestCase(testcase.TestCase):
                       self._json_replacer, message)
 
     def _run_request(self, url, method, headers, body):
-        """Run the http request and decode output."""
+        """Run the http request and decode output.
 
+        The call to make the request will catch a WSGIAppError from
+        wsgi_intercept so that the real traceback from a catastrophic
+        error in the intercepted app can be examined.
+        """
+
+        try:
             response, content = self.http.request(
                 url,
                 method=method,
                 headers=headers,
                 body=body
             )
+        except wsgi_intercept.WSGIAppError as exc:
+            # Extract and re-raise the wrapped exception.
+            six.reraise(exc.exception_type, exc.exception_value,
+                        exc.traceback)
 
         # Set headers and location attributes for follow on requests
         self.response = response

gabbi/gabbits_intercept/self.yaml

@@ -19,11 +19,11 @@ tests:
 
 - name: bogus method
   url: /
-  method: DIE
+  method: UNREAL
   status: 405
   response_headers:
       allow: GET, PUT, POST, DELETE, PATCH
-      x-gabbi-method: DIE
+      x-gabbi-method: UNREAL
       x-gabbi-url: $SCHEME://$NETLOC/
 
 - name: query returned
@@ -105,3 +105,9 @@ tests:
   xfail: true
   response_test:
       - 'CO"alpha": ["1"]'
+
+- name: test exception wrapper
+  desc: simple wsgi will raise exception
+  url: /
+  xfail: true
+  method: DIE

gabbi/simple_wsgi.py

@@ -51,6 +51,9 @@ class SimpleWsgi(object):
             ('X-Gabbi-url', request_url),
         ]
 
+        if request_method == 'DIE':
+            raise Exception('because you asked me to')
+
         if request_method not in METHODS:
             headers.append(
                 ('Allow', ', '.join(METHODS)))

test-failskip.sh

@@ -2,7 +2,7 @@
 # Run the tests and confirm that the stuff we expect to skip or fail
 # does.
 
-GREP_FAIL_MATCH='expected failures=3'
+GREP_FAIL_MATCH='expected failures=4'
 GREP_SKIP_MATCH='skips=2'
 
 python setup.py testr && \