Added more unittests to test_policy.py

tests/test_policy.py

+import os
 import unittest
+import paramiko
+
 from paramiko.client import RejectPolicy, WarningPolicy
-from webssh.policy import AutoAddPolicy, get_policy_dictionary
+from webssh.policy import AutoAddPolicy, get_policy_dictionary, load_host_keys
+from webssh.policy import get_policy_class, check_policy_setting
 
 
 class TestPolicy(unittest.TestCase):
@@ -11,3 +15,41 @@ class TestPolicy(unittest.TestCase):
         for cls in classes:
             val = dic[cls.__name__.lower()]
             self.assertIs(cls, val)
+
+    def test_load_host_keys(self):
+        path = '/path-not-exists'
+        host_keys = load_host_keys(path)
+        self.assertFalse(host_keys)
+
+        path = '/tmp'
+        host_keys = load_host_keys(path)
+        self.assertFalse(host_keys)
+
+    def test_get_policy_class(self):
+        keys = ['autoadd', 'reject', 'warning']
+        vals = [AutoAddPolicy, RejectPolicy, WarningPolicy]
+        for key, val in zip(keys, vals):
+            cls = get_policy_class(key)
+            self.assertIs(cls, val)
+
+        key = 'non-exists'
+        with self.assertRaises(ValueError):
+            get_policy_class(key)
+
+    def test_check_policy_setting(self):
+        host_keys_filename = './webssh/host_keys_test.db'
+        host_keys_settings = dict(
+            host_keys=paramiko.hostkeys.HostKeys(),
+            system_host_keys=paramiko.hostkeys.HostKeys(),
+            host_keys_filename=host_keys_filename
+        )
+
+        with self.assertRaises(ValueError):
+            check_policy_setting(RejectPolicy, host_keys_settings)
+
+        try:
+            os.unlink(host_keys_filename)
+        except OSError:
+            pass
+        check_policy_setting(AutoAddPolicy, host_keys_settings)
+        self.assertEqual(os.path.exists(host_keys_filename), True)