Merge ~racb/git-ubuntu:renameabledir-must-exist into git-ubuntu:master

[Robie Basak]

Make Jenkins happy

[Bryce Harrington (bryce)]

I like it!

review: Approve

[Server Team CI bot (server-team-bot)]

PASSED: Continuous integration, rev:1334cc5d6625a6eb8b7d7907fdde84dfbef11271
https://jenkins.ubuntu.com/server/job/git-ubuntu-ci/480/
Executed test runs:
    SUCCESS: VM Setup
    SUCCESS: Build
    SUCCESS: Unit Tests
    IN_PROGRESS: Declarative: Post Actions

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review: Approve (continuous-integration)

diff --git a/gitubuntu/git_repository.py b/gitubuntu/git_repository.py
index 002fa28..a0ae2e6 100644
--- a/gitubuntu/git_repository.py
+++ b/gitubuntu/git_repository.py
@@ -236,8 +236,17 @@ class RenameableDir:
         :param str path: the on-disk directory to wrap, which must exist. For
             symlinks, it is the symlink itself that must exist; the existence
             of a symlink's target does not matter.
+        :raises FileNotFoundError: if the path supplied does not exist.
         """
-        assert os.path.lexists(path)
+        # Ignore the return value of os.lstat(); this call is used to raise
+        # FileNotFoundError if the path does not exist (as required in the spec
+        # specified by the docstring), or succeed otherwise. The
+        # call for os.path.lexists() would use the same underlying system call
+        # anyway, so this is equivalent and this way we end up with a full
+        # FileNotFoundError exception created for us with all the correct
+        # parameters.
+        os.lstat(path)
+
         self._path = path
 
     @property
diff --git a/gitubuntu/git_repository_test.py b/gitubuntu/git_repository_test.py
index 773c947..a212080 100644
--- a/gitubuntu/git_repository_test.py
+++ b/gitubuntu/git_repository_test.py
@@ -341,6 +341,12 @@ def test_renameable_dir_hash_eq(tmpdir):
     assert rd1a != rd2
 
 
+def test_renameable_dir_must_exist(tmpdir):
+    """A RenameableDir should reject a path that doesn't exist"""
+    with pytest.raises(FileNotFoundError):
+        target.RenameableDir(tmpdir.join('a'))
+
+
 def test_fake_renameable_dir_basename():
     path = target.FakeRenameableDir('foo', None)
     assert path.basename == 'foo'