unittests: T2995: vyos_dict_search() must return None on non-existing keys

The current wversion unfortunately will raise a KeyError:

>>> data = {}
>>> vyos_dict_search('foo', data)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3/dist-packages/vyos/util.py", line 685, in vyos_dict_search
    return dict[path]
KeyError: 'foo'

1 files changed, 59 insertions, 0 deletions

diff --git a/src/tests/test_vyos_dict_search.py b/src/tests/test_vyos_dict_search.py
new file mode 100644
index 000000000..ef338d46f
--- /dev/null
+++ b/src/tests/test_vyos_dict_search.py
@@ -0,0 +1,59 @@
+#!/usr/bin/env python3
+#
+# Copyright (C) 2020 VyOS maintainers and contributors
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License version 2 or later as
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+import unittest
+from unittest import TestCase
+
+from vyos.util import vyos_dict_search
+
+data = {
+    'string': 'fooo',
+    'nested': {'string': 'bar', 'empty': '', 'list': ['foo', 'bar']},
+    'list': ['bar', 'baz'],
+    'dict': {'key_1': {}, 'key_2': 'vyos'}
+}
+
+class TestDictSearch(TestCase):
+    def setUp(self):
+        pass
+
+    def test_non_existing_keys(self):
+        """ TestDictSearch: Return False when querying for non-existent key """
+        self.assertFalse(vyos_dict_search('non_existing', data))
+
+    def test_string(self):
+        """ TestDictSearch: Return value when querying string """
+        self.assertEqual(vyos_dict_search('string', data), data['string'])
+
+    def test_list(self):
+        """ TestDictSearch: Return list items when querying list """
+        self.assertEqual(vyos_dict_search('list', data), data['list'])
+
+    def test_dict_key_value(self):
+        """ TestDictSearch: Return dictionary keys value when value is present """
+        self.assertEqual(vyos_dict_search('dict.key_2', data), data['dict']['key_2'])
+
+    def test_nested_dict_key_value(self):
+        """ TestDictSearch: Return string value of last key when querying for a nested string """
+        self.assertEqual(vyos_dict_search('nested.string', data), data['nested']['string'])
+
+    def test_nested_dict_key_empty(self):
+        """ TestDictSearch: Return False when querying for a nested string whose last key is empty """
+        self.assertFalse(vyos_dict_search('nested.empty', data))
+
+    def test_nested_list(self):
+        """ TestDictSearch: Return list items when querying nested list """
+        self.assertEqual(vyos_dict_search('nested.list', data), data['nested']['list'])