gh-93839: Move Lib/unttest/test/ to Lib/test/test_unittest/ (#94043)

* Move Lib/unittest/test/ to Lib/test/test_unittest/
* Remove Lib/test/test_unittest.py
* Replace unittest.test with test.test_unittest
* Remove unittest.load_tests()
* Rewrite unittest __init__.py and __main__.py
* Update build system, CODEOWNERS, and wasm_assets.py

Lib/test/test_unittest/_test_warnings.py

@@ -0,0 +1,73 @@
+# helper module for test_runner.Test_TextTestRunner.test_warnings
+
+"""
+This module has a number of tests that raise different kinds of warnings.
+When the tests are run, the warnings are caught and their messages are printed
+to stdout.  This module also accepts an arg that is then passed to
+unittest.main to affect the behavior of warnings.
+Test_TextTestRunner.test_warnings executes this script with different
+combinations of warnings args and -W flags and check that the output is correct.
+See #10535.
+"""
+
+import sys
+import unittest
+import warnings
+
+def warnfun():
+    warnings.warn('rw', RuntimeWarning)
+
+class TestWarnings(unittest.TestCase):
+    # unittest warnings will be printed at most once per type (max one message
+    # for the fail* methods, and one for the assert* methods)
+    def test_assert(self):
+        self.assertEquals(2+2, 4)
+        self.assertEquals(2*2, 4)
+        self.assertEquals(2**2, 4)
+
+    def test_fail(self):
+        self.failUnless(1)
+        self.failUnless(True)
+
+    def test_other_unittest(self):
+        self.assertAlmostEqual(2+2, 4)
+        self.assertNotAlmostEqual(4+4, 2)
+
+    # these warnings are normally silenced, but they are printed in unittest
+    def test_deprecation(self):
+        warnings.warn('dw', DeprecationWarning)
+        warnings.warn('dw', DeprecationWarning)
+        warnings.warn('dw', DeprecationWarning)
+
+    def test_import(self):
+        warnings.warn('iw', ImportWarning)
+        warnings.warn('iw', ImportWarning)
+        warnings.warn('iw', ImportWarning)
+
+    # user warnings should always be printed
+    def test_warning(self):
+        warnings.warn('uw')
+        warnings.warn('uw')
+        warnings.warn('uw')
+
+    # these warnings come from the same place; they will be printed
+    # only once by default or three times if the 'always' filter is used
+    def test_function(self):
+
+        warnfun()
+        warnfun()
+        warnfun()
+
+
+
+if __name__ == '__main__':
+    with warnings.catch_warnings(record=True) as ws:
+        # if an arg is provided pass it to unittest.main as 'warnings'
+        if len(sys.argv) == 2:
+            unittest.main(exit=False, warnings=sys.argv.pop())
+        else:
+            unittest.main(exit=False)
+
+    # print all the warning messages collected
+    for w in ws:
+        print(w.message)