def test_empty(): assert character_whitelist('', 'XYZ') == ''
def test_nomatch(): x = 'rgerg erthgtrerw goirehgfj8934 tg453rg 34tg' assert character_whitelist(x, 'XYZ') == ''
def test_xyyzy(): x = 'regrsXnl je45n34gYt35go48uyZghZ345hg 4t3Y45yt4 ' assert character_whitelist(x, 'XYZ') == 'XYZZY'