bpo-28850: Fix PrettyPrinter.format overrides ignored for contents of small containers (GH-22120)

diff --git a/Lib/test/test_pprint.py b/Lib/test/test_pprint.py
index 8ee18e8..c4a8578 100644
--- a/Lib/test/test_pprint.py
+++ b/Lib/test/test_pprint.py
@@ -453,12 +453,23 @@ class AdvancedNamespace(types.SimpleNamespace): pass
                   dog=8)""")
 
     def test_subclassing(self):
+        # length(repr(obj)) > width
         o = {'names with spaces': 'should be presented using repr()',
              'others.should.not.be': 'like.this'}
         exp = """\
 {'names with spaces': 'should be presented using repr()',
  others.should.not.be: like.this}"""
-        self.assertEqual(DottedPrettyPrinter().pformat(o), exp)
+
+        dotted_printer = DottedPrettyPrinter()
+        self.assertEqual(dotted_printer.pformat(o), exp)
+
+        # length(repr(obj)) < width
+        o1 = ['with space']
+        exp1 = "['with space']"
+        self.assertEqual(dotted_printer.pformat(o1), exp1)
+        o2 = ['without.space']
+        exp2 = "[without.space]"
+        self.assertEqual(dotted_printer.pformat(o2), exp2)
 
     def test_set_reprs(self):
         self.assertEqual(pprint.pformat(set()), 'set()')