Fix cloning a repository with a particular branch to checkout

We were missing a cast to bytes. Add a test for this option as well and
remove the old commented-out test for checkout_branch, which is
superseded by this one and whose last bit seemed confused about what the
option means.

This fixes #399

pygit2/__init__.py

@@ -154,7 +154,7 @@ def clone_repository(
     # We need to keep the ref alive ourselves
     checkout_branch_ref = None
     if branch:
-        checkout_branch_ref = ffi.new('char []', branch)
+        checkout_branch_ref = ffi.new('char []', to_bytes(branch))
         opts.checkout_branch = checkout_branch_ref
 
     remote_name_ref = ffi.new('char []', to_bytes(remote_name))

test/test_repository.py

@@ -428,6 +428,17 @@ def test_clone_with_credentials(self):
 
         self.assertFalse(repo.is_empty)
 
+    def test_clone_with_checkout_branch(self):
+        # create a test case which isolates the remote
+        test_repo = clone_repository('./test/data/testrepo.git',
+                                     os.path.join(self._temp_dir, 'testrepo-orig.git'),
+                                     bare=True)
+        test_repo.create_branch('test', test_repo[test_repo.head.target])
+        repo = clone_repository(test_repo.path,
+                                os.path.join(self._temp_dir, 'testrepo.git'),
+                                checkout_branch='test', bare=True)
+        self.assertEqual(repo.lookup_reference('HEAD').target, 'refs/heads/test')
+
     # FIXME The tests below are commented because they are broken:
     #
     # - test_clone_push_url: Passes, but does nothing useful.
@@ -437,8 +448,6 @@ def test_clone_with_credentials(self):
     #
     # - test_clone_push_spec: Passes, but does nothing useful.
     #
-    # - test_clone_checkout_branch: Fails, because the test fixture does not
-    #   have any branch named "test"
 
 #   def test_clone_push_url(self):
 #       repo_path = "./test/data/testrepo.git/"
@@ -470,15 +479,5 @@ def test_clone_with_credentials(self):
 #       # not sure how to test this either... couldn't find pushspec
 #       # self.assertEqual(repo.remotes[0].fetchspec, "refs/heads/test")
 
-#   def test_clone_checkout_branch(self):
-#       repo_path = "./test/data/testrepo.git/"
-#       repo = clone_repository(repo_path, self._temp_dir,
-#                               checkout_branch="test")
-#       self.assertFalse(repo.is_empty)
-#       # FIXME: When pygit2 supports retrieving the current branch,
-#       # enable this test
-#       # self.assertEqual(repo.remotes[0].current_branch, "test")
-
-
 if __name__ == '__main__':
     unittest.main()