Seems there is the same cause of the failure of test_curses on OpenBSD.

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ERROR: test_window_funcs (test.test_curses.TestCurses) (meth='window.getkey')
Test the methods of windows
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Traceback (most recent call last):
  File "/home/serhiy/py/cpython3.7/Lib/test/test_curses.py", line 99, in test_window_funcs
    meth()
ValueError: chr() arg not in range(0x110000)

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FAIL: test_unget_wch (test.test_curses.TestCurses)
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Traceback (most recent call last):
  File "/home/serhiy/py/cpython3.7/Lib/test/test_curses.py", line 355, in test_unget_wch
    self.assertEqual(read, ch)
AssertionError: -61 != 'é'

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System ncurses version is 5.7.