def expect_next from p (str):
    expect /(.*)/ from p capture line
    guard (line == str)

test Test:
    node n
    shell on n as p:
        cat

    send "a1" to p
    send "b" to p
    send "x" to p
    expect /x/ from p

    flush from p matching /a.*/
    send "a2" to p
    send "c" to p

    expect_next "b" from p
    expect_next "a2" from p
    expect_next "c" from p

    send "d" to p
    send "e" to p
    send "f" to p
    send "x" to p
    expect /x/ from p
    flush from p
    send "g" to p
    expect_next "g" from p