gh-100933: Improve check_element helper in test_xml_etree (#100934)

Items checked by this test are always `str` and `dict` instances.

Lib/test/test_xml_etree.py

@@ -203,25 +203,6 @@ def serialize_check(self, elem, expected):
  def test_interface(self):
  # Test element tree interface.
 
- def check_string(string):
- len(string)
- for char in string:
- self.assertEqual(len(char), 1,
- msg="expected one-character string, got %r" % char)
- new_string = string + ""
- new_string = string + " "
- string[:0]
-
- def check_mapping(mapping):
- len(mapping)
- keys = mapping.keys()
- items = mapping.items()
- for key in keys:
- item = mapping[key]
- mapping["key"] = "value"
- self.assertEqual(mapping["key"], "value",
- msg="expected value string, got %r" % mapping["key"])
-
  def check_element(element):
  self.assertTrue(ET.iselement(element), msg="not an element")
  direlem = dir(element)
@@ -231,12 +212,12 @@ def check_element(element):
  self.assertIn(attr, direlem,
  msg='no %s visible by dir' % attr)
 
- check_string(element.tag)
- check_mapping(element.attrib)
+ self.assertIsInstance(element.tag, str)
+ self.assertIsInstance(element.attrib, dict)
  if element.text is not None:
- check_string(element.text)
+ self.assertIsInstance(element.text, str)
  if element.tail is not None:
- check_string(element.tail)
+ self.assertIsInstance(element.tail, str)
  for elem in element:
  check_element(elem)