Merge ~pjdc/ubuntu-mirror-charm/+git/ubuntu-mirror-charm:test-ensure-symlink into ubuntu-mirror-charm:master

[Paul Collins]

add test_ensure_symlink

[🤖 Canonical IS Merge Bot (canonical-is-mergebot)]

This merge proposal is being monitored by mergebot. Change the status to Approved to merge.

[Haw Loeung (hloeung)]

LGTM

review: Approve (+1)

[🤖 Canonical IS Merge Bot (canonical-is-mergebot)]

Change successfully merged at revision 0a789954e76103aed38d084c46771dcc56b61c7b

diff --git a/tests/unit/test_charm.py b/tests/unit/test_charm.py
index 31764d4..1622eb1 100644
--- a/tests/unit/test_charm.py
+++ b/tests/unit/test_charm.py
@@ -7,6 +7,8 @@ import unittest
 from base64 import b64encode
 from copy import deepcopy
 from mock import mock_open, patch
+from tempfile import mkdtemp
+from shutil import rmtree
 
 import Config  # for mockery
 import hooks   # noqa: F401; for mockery
@@ -16,6 +18,7 @@ from hooks import (
     add_bind_mount,
     collect_mountpoints,
     configure_triggers,
+    ensure_symlink,
     extract_ssh_public_key,
     generate_disk_check,
     get_managed_mounts,
@@ -248,3 +251,30 @@ class TestUbuntuMirrorCharm(unittest.TestCase):
             '}\n',
             perms=0o444,
         )
+
+    def test_ensure_symlink(self):
+        try:
+            tmpdir = mkdtemp()  # Python 2 doesn't have tempfile.TemporaryDirectory
+            target = os.path.join(tmpdir, 'target')
+            os.mkdir(target)
+            new_target = os.path.join(tmpdir, 'new_target')
+            os.mkdir(new_target)
+            link_path = os.path.join(tmpdir, 'link_path')
+
+            # Symlink creation works.
+            self.assertIsNone(ensure_symlink(target, link_path))
+            self.assertEqual(target, os.readlink(link_path))
+
+            # Symlink creation is idempotent.
+            self.assertIsNone(ensure_symlink(target, link_path))
+            self.assertEqual(target, os.readlink(link_path))
+
+            # Symlink replacement works.
+            self.assertIsNone(ensure_symlink(new_target, link_path))
+            self.assertEqual(new_target, os.readlink(link_path))
+
+            # Replacing a non-symlink throws an exception.
+            with self.assertRaises(Exception):
+                ensure_symlink(target, new_target)
+        finally:
+            rmtree(tmpdir)