dist/pythonlibs: provide unittest TestCase wrapper for testrunner

I had this idea when implementing #10382 and #10392 as I introduced a
very similar structure to python's standard unittests in those and it
could also reduce some code duplication between those two tests.

dist/pythonlibs/testrunner/__init__.py

@@ -13,6 +13,7 @@ from traceback import print_tb
 import pexpect
 
 from .spawn import find_exc_origin, setup_child, teardown_child
+from .unittest import PexpectTestCase   # noqa, F401 expose to users
 
 
 def run(testfunc, timeout=10, echo=True, traceback=False):

dist/pythonlibs/testrunner/unittest.py

@@ -0,0 +1,23 @@
+# Copyright (C) 2018-19 Freie Universität Berlin
+#
+# This file is subject to the terms and conditions of the GNU Lesser
+# General Public License v2.1. See the file LICENSE in the top level
+# directory for more details.
+
+import unittest
+from testrunner import setup_child, teardown_child
+
+
+class PexpectTestCase(unittest.TestCase):
+    TIMEOUT = 10
+    LOGFILE = None
+
+    """A unittest TestCase providing a pexpect spawn object to it's tests
+    """
+    @classmethod
+    def setUpClass(cls):
+        cls.spawn = setup_child(cls.TIMEOUT, logfile=cls.LOGFILE)
+
+    @classmethod
+    def tearDownClass(cls):
+        teardown_child(cls.spawn)