test: convert test/test_namespace/test_namespace.py to pytest (#2060)

Convert the remaining unittest based classes to pytest.

test/test_namespace/test_namespace.py

@@ -1,7 +1,5 @@
-import unittest
 from contextlib import ExitStack
 from typing import Any, Optional, Type, Union
-from unittest.case import expectedFailure
 from warnings import warn
 
 import pytest
@@ -22,7 +20,7 @@
 from rdflib.term import URIRef
 
 
-class NamespaceTest(unittest.TestCase):
+class TestNamespace:
     def setup_method(self, method):
         self.ns_str = "http://example.com/name/space/"
         self.ns = Namespace(self.ns_str)
@@ -48,7 +46,7 @@ def test_iri(self):
         assert ns["jörn"].startswith(ns)
 
 
-class ClosedNamespaceTest(unittest.TestCase):
+class TestClosedNamespace:
     def setup_method(self, method):
         self.ns_str = "http://example.com/name/space/"
         self.ns = ClosedNamespace(self.ns_str, ["a", "b", "c"])
@@ -57,7 +55,7 @@ def test_repr(self):
         # NOTE: this assumes ns_str has no characthers that need escaping
         assert self.ns_str in f"{self.ns!r}"
 
-    @expectedFailure
+    @pytest.mark.xfail
     def test_repr_ef(self):
         """
         This fails because ClosedNamespace repr does not represent the second argument