copy data from static variable instead of use it directly to prevent caching.

also update test cases to verfiy this issue.

Fixes: #994
https://pagure.io/koji/issue/994

tests/test_hub/test_rpmdiff.py

@@ -1,6 +1,7 @@
 from __future__ import absolute_import
 import copy
 import mock
+import os
 try:
     import unittest2 as unittest
 except ImportError:
@@ -37,6 +38,30 @@ class TestRPMDiff(unittest.TestCase):
         Rpmdiff.assert_called_once_with('basepath/12/1234/foo', 'basepath/13/1345/bar', ignore='S5TN')
         d.textdiff.assert_called_once_with()
 
+    def test_rpmdiff_real_target(self):
+        data_path = os.path.abspath("tests/test_hub/data/rpms")
+
+        # the only differences between rpm1 and rpm2 are 1) create time 2) file name
+        rpm1 = os.path.join(data_path, 'test-pkg-1.0.0-1.el7.noarch.rpm')
+        rpm2 = os.path.join(data_path, 'test-pkg-1.0.0-1.fc24.noarch.rpm')
+
+        diff_output = "..........T /usr/share/test-pkg/test-doc01.txt\n" + \
+                      "..........T /usr/share/test-pkg/test-doc02.txt\n" + \
+                      "..........T /usr/share/test-pkg/test-doc03.txt\n" + \
+                      "..........T /usr/share/test-pkg/test-doc04.txt"
+
+        # case 1. no ignore option, timestamp is different
+        # perform twice check to verify issue: #994
+        for _ in range(0, 2):
+            d = koji.rpmdiff.Rpmdiff(rpm1, rpm2)
+            self.assertEqual(d.textdiff(), diff_output)
+
+        # case 2. ignore timestamp, two rpms should be the same
+        # perform twice check to verify issue: #994
+        for r in range(0, 2):
+            d = koji.rpmdiff.Rpmdiff(rpm1, rpm2, ignore='S5TN')
+            self.assertEqual(d.textdiff(), '')
+
 class TestCheckNoarchRpms(unittest.TestCase):
     @mock.patch('kojihub.rpmdiff')
     def test_check_noarch_rpms_empty_invocation(self, rpmdiff):