This test might have an error.

For input

 <test id="p1800" regex="( a | ( bc ) ) {0,0} ? xyz" flags="x" input="xyz" result="y"/>

the regex atom is ( a | ( bc ) )

and the quantifier is {0,0}.  This leaves ? unmatched.

[3]   	piece	   ::=   	atom quantifier?
[4]   	quantifier	   ::=   	[?*+] | ( '{' quantity '}' )

Incidentally, the content of the "error" attribute should probably have curly brackets in it.