Issue #21881: Just omit tests for platform-specific NaN representation in test_tcl.

Lib/test/test_tcl.py

@@ -420,11 +420,9 @@ class TclTest(unittest.TestCase):
             self.assertEqual(passValue(float('inf')), float('inf'))
             self.assertEqual(passValue(-float('inf')), -float('inf'))
         else:
-            f = passValue(float('nan'))
-            self.assertIsInstance(f, str)
-            self.assertEqual(f.lower()[:3], 'nan')
             self.assertEqual(float(passValue(float('inf'))), float('inf'))
             self.assertEqual(float(passValue(-float('inf'))), -float('inf'))
+            # XXX NaN representation can be not parsable by float()
         self.assertEqual(passValue((1, '2', (3.4,))),
                          (1, '2', (3.4,)) if self.wantobjects else '1 2 3.4')
 
@@ -449,8 +447,6 @@ class TclTest(unittest.TestCase):
             expected = float(expected)
             self.assertAlmostEqual(float(actual), expected,
                                    delta=abs(expected) * 1e-10)
-        def starts_with(actual, expected):
-            self.assertEqual(actual.lower()[:len(expected)], expected)
 
         check(True, '1')
         check(False, '0')
@@ -474,7 +470,7 @@ class TclTest(unittest.TestCase):
             check(f, f, eq=float_eq)
         check(float('inf'), 'Inf', eq=float_eq)
         check(-float('inf'), '-Inf', eq=float_eq)
-        check(float('nan'), 'nan', eq=starts_with)
+        # XXX NaN representation can be not parsable by float()
         check((), '')
         check((1, (2,), (3, 4), '5 6', ()), '1 2 {3 4} {5 6} {}')