18 is($x // 0, 1, ' // : left-hand operand defined');
21 is($x // 1, 1, ' // : left-hand operand undef');
24 is($x // 0, '', ' // : left-hand operand defined but empty');
27 is(($x err 0), 1, ' err: left-hand operand defined');
30 is(($x err 1), 1, ' err: left-hand operand undef');
33 is(($x err 0), '', ' err: left-hand operand defined but empty');
37 is($x, 1, ' //=: left-hand operand undefined');
40 is($x, 1, ' //=: left-hand operand defined');
44 is($x, '', ' //=: left-hand operand defined but empty');