run_unittests: Add a chdir context manager

Because seriously

run_unittests.py

@@ -76,6 +76,13 @@ from run_tests import (
 
 URLOPEN_TIMEOUT = 5
 
+@contextmanager
+def chdir(path: str):
+    curdir = os.getcwd()
+    os.chdir(path)
+    yield
+    os.chdir(curdir)
+
 
 def get_dynamic_section_entry(fname, entry):
     if is_cygwin() or is_osx():
@@ -5861,7 +5868,7 @@ class LinuxlikeTests(BasePlatformTests):
         testdir = os.path.join(self.common_test_dir, testdir)
         subdir = os.path.join(testdir, subdir_path)
         curdir = os.getcwd()
-        os.chdir(subdir)
+        with chdir(subdir):
             # Can't distribute broken symlinks in the source tree because it breaks
             # the creation of zipapps. Create it dynamically and run the test by
             # hand.
@@ -5878,7 +5885,6 @@ class LinuxlikeTests(BasePlatformTests):
                 self.assertFalse(os.path.isfile(link), msg=link)
             finally:
                 os.remove(os.path.join(subdir, 'invalid-symlink.txt'))
-            os.chdir(curdir)
 
     def test_install_subdir_symlinks(self):
         self.install_subdir_invalid_symlinks('62 install subdir', os.path.join('sub', 'sub1'))