Always close files in distutils code and tests (#10252).
diff --git a/Lib/distutils/tests/test_dir_util.py b/Lib/distutils/tests/test_dir_util.py
index a1647fb..aa9f9eb 100644
--- a/Lib/distutils/tests/test_dir_util.py
+++ b/Lib/distutils/tests/test_dir_util.py
@@ -88,8 +88,10 @@
         mkpath(self.target, verbose=0)
         a_file = os.path.join(self.target, 'ok.txt')
         f = open(a_file, 'w')
-        f.write('some content')
-        f.close()
+        try:
+            f.write('some content')
+        finally:
+            f.close()
 
         wanted = ['copying %s -> %s' % (a_file, self.target2)]
         copy_tree(self.target, self.target2, verbose=1)