test_builtin_casters.py test_string_view: Python 2 c++17, c++2a compa…

[rwgk]

…tibility.

Tested with 2.7.18rc1, built with Py_UNICODE_SIZE 4.
Change also tested with Python 3.8.

[YannickJadoul]

Same is done here:

pybind11/tests/test_builtin_casters.py

Lines 63 to 85 in a38dfee

	assertm.ord_char16(u'a') ==0x61
	assertm.ord_char16(u'é') ==0xE9
	assertm.ord_char16_lv(u'ê') ==0xEA
	assertm.ord_char16(u'Ā') ==0x100
	assertm.ord_char16(u'‽') ==0x203d
	assertm.ord_char16(u'♥') ==0x2665
	assertm.ord_char16_lv(u'♡') ==0x2661
	withpytest.raises(ValueError) asexcinfo:
	assertm.ord_char16(u'🎂') ==0x1F382# requires surrogate pair
	assertstr(excinfo.value) ==toobig_message(0x10000)
	withpytest.raises(ValueError) asexcinfo:
	assertm.ord_char16(u'aa')
	assertstr(excinfo.value) ==toolong_message
	assertm.ord_char32(u'a') ==0x61
	assertm.ord_char32(u'é') ==0xE9
	assertm.ord_char32(u'Ā') ==0x100
	assertm.ord_char32(u'‽') ==0x203d
	assertm.ord_char32(u'♥') ==0x2665
	assertm.ord_char32(u'🎂') ==0x1F382
	withpytest.raises(ValueError) asexcinfo:
	assertm.ord_char32(u'aa')
	assertstr(excinfo.value) ==toolong_message

So seems great to me! :-)

[rwgk]

Thanks a lot Yannick for pointing out the other test using the same approach, I missed that. Since there is a precedence for what I'm doing I'll merge this PR now, to get a baseline for my work on PR #2256.