Add support for failing test proposed in #42

pygtail/core.py

@@ -97,6 +97,12 @@ def __init__(self, filename, offset_file=None, paranoid=False, copytruncate=True
                 # might have been rotated.
                 # Look for the rotated file and process that if we find it.
                 self.rotated_logfile = self._determine_rotated_logfile()
+                # If copytruncate is enabled and we can't find the rotated logfile, all we can do is reset.
+                if self.copytruncate and self.rotated_logfile is None:
+                    sys.stderr.write("[pygtail] [WARN] log file was rotated to unknown location. Resetting.\n")
+                    self.offset = 0
+                    self.update_offset_file()
+
 
     def __del__(self):
         if self._filehandle():

pygtail/test/test_pygtail.py

@@ -323,9 +323,15 @@ def test_renamecreate_unknown_rotated_name(self):
         self.append(new_lines[0])
         self.append(new_lines[1])
         # reopen using Pytgail
+        sys.stderr = captured = io.BytesIO() if PY2 else io.StringIO()
         pygtail = Pygtail(self.logfile.name)
+        captured_value = captured.getvalue()
+        sys.stderr = sys.__stderr__
+        assert_class = self.assertRegex if sys.version_info >= (3, 1) else self.assertRegexpMatches
+        assert_class(captured_value, r".*?\bWARN\b.*?\bResetting\b.*")
         self.assertEqual(pygtail.read(), ''.join(new_lines))
 
+
     def test_full_lines(self):
         """
         Tests lines are logged only when they have a new line at the end. This is useful to ensure that log lines