ENH: added a unittest demonstrating the arithm progression sum effect

See https://github.com/fail2ban/fail2ban/issues/17 for more information

To run that only test (to fail) you can use nose:

nosetests -s -v testcases/filtertestcase.py:FileFilterTests.testRecycledLog

testcases/filtertestcase.py

@@ -231,3 +231,66 @@ class DNSUtilsTests(unittest.TestCase):
 		for s in bogus:
 			res = DNSUtils.textToIp(s)
 			self.assertEqual(res, [])
+
+
+import os, tempfile
+
+class FileFilterTests(unittest.TestCase):
+
+	def testRecycledLog(self):
+
+		class RecycledLog:
+			"""Helper class to immitate few kinds of logs
+
+			physical file gets removed in __del__
+			"""
+			def __init__(self, filename, n=None):
+				"""
+				Parameters
+				----------
+				filename : str
+				  Name of the file
+				n : int or None
+				  if None, no recycling happning so it 'looks' like a
+				  regular log which just appends new lines (although
+				  technically different since it gets rewritten
+				  entirely upon each new entry)
+				  """
+				self.filename = filename
+				self.n = n
+				self._entries = []
+				# initiate the file so it is not empty
+				open(self.filename, 'w').close()
+
+			def __del__(self):
+				os.remove(self.filename)
+
+			def write(self, s):
+				self._entries += [s]
+				if self.n:
+					# and now 'shrink' it if necessary
+					self._entries = self._entries[max(0, len(self._entries)-self.n):]
+				# rewrite the file with "new" entries
+				open(self.filename, 'w').write('\n'.join(self._entries)+'\n')
+
+		#logfile = '/tmp/1.dat'
+		_, logfile = tempfile.mkstemp('-f2b-test')
+		for n in (0, 3):	  # shrink file and don't
+			log = RecycledLog(logfile, n)
+
+			ff = FilterPoll(None)
+			ff.addLogPath(logfile)
+			ff.setActive(True)
+			ff.setFindTime(3600*24*365*20)	# long enough to run it simply via nosetests
+											# ATM without adjusting MyTime
+			ff.setMaxRetry(2)				# fail on having 2
+			ff.addFailRegex("FAILED <HOST>$")
+			for i in range(10):
+				log.write("Aug 14 11:59:59 FAILED 192.0.43.%d" % i)
+				ff.getFailures(logfile)
+				ff_status = ff.status()
+				assert(ff_status[0][0] == 'Currently failed')
+				assert(ff_status[1][0] == 'Total failed')
+				self.assertEqual(ff_status[0][1], ff_status[1][1])
+				#print ff_status
+			del log