Strip irrelevant lines from test output

It may happen that aptly retries to download data during tests (maybe because
of a network issue), but our fixtures doesn't account for it. So, we strip
those irrelevant lines before comparison.

system/lib.py

@@ -8,6 +8,7 @@ import json
 import subprocess
 import os
 import posixpath
+import re
 import shlex
 import shutil
 import string
@@ -279,6 +280,15 @@ class BaseTest(object):
     def get_gold(self, gold_name="gold"):
         return self.gold_processor(open(self.get_gold_filename(gold_name), "r").read())
 
+    def strip_retry_lines(self, s):
+        for prefix in (
+                'Following redirect',
+                'Error downloading',
+                'Retrying',
+        ):
+            s = re.sub(r'{}.*\n'.format(prefix), '', s)
+        return s
+
     def check_output(self):
         try:
             self.verify_match(self.get_gold(), self.output,
@@ -382,6 +392,10 @@ class BaseTest(object):
             a = match_prepare(a)
             b = match_prepare(b)
 
+        # Make sure there is something to compare after `match_prepare`
+        if not a or not b:
+            raise Exception("content empty")
+
         if a != b:
             diff = "".join(difflib.unified_diff(
                 [l + "\n" for l in a.split("\n")], [l + "\n" for l in b.split("\n")]))

system/t04_mirror/create.py

@@ -362,6 +362,9 @@ class CreateMirror27Test(BaseTest):
     """
     runCmd = "aptly mirror create --ignore-signatures mirror27 http://linux.dell.com/repo/community/ubuntu wheezy openmanage/740"
 
+    def outputMatchPrepare(self, s):
+        return self.strip_retry_lines(s)
+
     def check(self):
         self.check_output()
         self.check_cmd_output("aptly mirror show mirror27", "mirror_show")