patchtest: Add tests from patchtest oe repo

Copy the core components of the patchtest-oe repo into
meta/lib/patchtest in oe-core.

(From OE-Core rev: 257f64f4e4414b78981104aec132b067beb5a92a)

Signed-off-by: Trevor Gamblin <tgamblin@baylibre.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/patchtest/tests/test_mbox_format.py

@@ -0,0 +1,16 @@
+# Checks correct parsing of mboxes
+#
+# Copyright (C) 2016 Intel Corporation
+#
+# SPDX-License-Identifier: GPL-2.0
+
+import base
+import re
+
+class MboxFormat(base.Base):
+
+    def test_mbox_format(self):
+        if self.unidiff_parse_error:
+            self.fail('Series cannot be parsed correctly due to malformed diff lines',
+                      'Create the series again using git-format-patch and ensure it can be applied using git am',
+                      data=[('Diff line', re.sub('^.+:\s(?<!$)','',self.unidiff_parse_error))])