case foo {
    f(?=o)oo {}
    .* { echo fail 1 }
}

case foo {
    fo(?=x)o { echo fail 2 }
    .* { }
}

fun match {
    set res = $($1 $2)
    if [ $res != $3 ] {
        echo "match $1 $2: expected $3, got $res"
    }
}

fun x0 {
    case $1 {
        a(?=b). { echo yes }
        .* { echo no }
    }
}
match x0 aa no
match x0 aaa no
match x0 ab yes

fun x1 {
    case $1 {
        x(?=foo)(?=...bar).* { echo yes }
        .* { echo no }
    }
}
match x1 xfoobar yes
match x1 xfoobar_some_more_stuff yes
match x1 x___bar no
match x1 xfoo___ no
match x1 xfoo    no

fun x2 {
    case $1 {
        (?=foo).*(?=bar).* { echo yes }
        .* { echo no }
    }
}
match x2 foobar yes
match x2 foobarbaz yes
match x2 barfoo no
match x2 foobaz no
match x3 foo_stuff_bar yes
match x3 foo_stuff_bar_more_stuff yes

fun x3 {
    case $1 {
        (?=abc).*(?=cde).* { echo yes }
        .* { echo no }
    }
}
match x3 abc_cde yes
match x3 abcde yes
match x3 abcdef yes
match x3 abde no