tests: run FD and thread checks on every test case.

Trying to hunt down weirdness on Azure.

tests/testlib.py

@@ -282,11 +282,10 @@ class TestCase(unittest2.TestCase):
         'mitogen.master.join_thread_async'
     ])
 
-    @classmethod
-    def _teardown_check_threads(cls):
+    def _teardown_check_threads(self):
         counts = {}
         for thread in threading.enumerate():
-            assert thread.name in cls.ALLOWED_THREADS, \
+            assert thread.name in self.ALLOWED_THREADS, \
                 'Found thread %r still running after tests.' % (thread.name,)
             counts[thread.name] = counts.get(thread.name, 0) + 1
 
@@ -294,20 +293,18 @@ class TestCase(unittest2.TestCase):
             assert counts[name] == 1, \
                 'Found %d copies of thread %r running after tests.' % (name,)
 
-    @classmethod
-    def _teardown_check_fds(cls):
+    def _teardown_check_fds(self):
         mitogen.core.Latch._on_fork()
-        if get_fd_count() != cls._fd_count_before:
+        if get_fd_count() != self._fd_count_before:
             import os; os.system('lsof -p %s' % (os.getpid(),))
             assert 0, "%s leaked FDs. Count before: %s, after: %s" % (
-                cls, cls._fd_count_before, get_fd_count(),
+                self, self._fd_count_before, get_fd_count(),
             )
 
-    @classmethod
-    def tearDownClass(cls):
-        super(TestCase, cls).tearDownClass()
-        cls._teardown_check_threads()
-        cls._teardown_check_fds()
+    def tearDown(self):
+        self._teardown_check_threads()
+        self._teardown_check_fds()
+        super(TestCase, self).tearDown()
 
     def assertRaises(self, exc, func, *args, **kwargs):
         """Like regular assertRaises, except return the exception that was