fix tests that assumed default initial branch setting

Author: SonOfLilit

Diff for: test/test_diff.py

@@ -51,7 +51,7 @@ def _assert_diff_format(self, diffs):
     @with_rw_directory
     def test_diff_with_staged_file(self, rw_dir):
         # SET UP INDEX WITH MULTIPLE STAGES
-        r = Repo.init(rw_dir)
+        r = Repo.init(rw_dir, initial_branch="master")
         fp = osp.join(rw_dir, "hello.txt")
         with open(fp, "w") as fs:
             fs.write("hello world")

Diff for: test/test_repo.py

@@ -1193,7 +1193,7 @@ def test_remote_method(self):
     @with_rw_directory
     def test_empty_repo(self, rw_dir):
         """Assure we can handle empty repositories"""
-        r = Repo.init(rw_dir, mkdir=False)
+        r = Repo.init(rw_dir, mkdir=False, initial_branch="master")
         # It's ok not to be able to iterate a commit, as there is none.
         self.assertRaises(ValueError, r.iter_commits)
         self.assertEqual(r.active_branch.name, "master")
@@ -1352,7 +1352,7 @@ def test_git_work_tree_env(self, rw_dir):
 
     @with_rw_directory
     def test_rebasing(self, rw_dir):
-        r = Repo.init(rw_dir)
+        r = Repo.init(rw_dir, initial_branch="master")
         fp = osp.join(rw_dir, "hello.txt")
         r.git.commit(
             "--allow-empty",