FAIL: test_find_periodic_pattern (test.test_userstring.UserStringTest.test_find_periodic_pattern) (p='', text='')
Cover the special path for periodic patterns.
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Traceback (most recent call last):
  File "/home/runner/work/cpython/cpython-ro-srcdir/Lib/test/string_tests.py", line 341, in test_find_periodic_pattern
    self.checkequal(reference_find(p, text),
  File "/home/runner/work/cpython/cpython-ro-srcdir/Lib/test/test_userstring.py", line 24, in checkequal
    self.assertEqual(
AssertionError: -1 != 0