busybox/shell/hush_test/hush-misc/compound.tests

echo new group
echo 0;  { :; }
echo 1;  { : ;}
echo 2; ({ :; })
echo 3; ({ : ;})
echo 4;  ( :  )
echo 5;  ( :; )
echo 6;  ( : ;)
# not sure if POSIX requires these, but bash accepts them ...
#echo 7; {( :  )}
#echo 8; {( :; )}
#echo 9; {( : ;)}

echo new group
#echo 0;  {(:);}

echo new group
echo 0;  (:)
echo 1;  (:;)
echo 2;  (:);
echo 3;  (:;);