Test fails on mac

[hibariya]

This probrem seems to be independent from #8.

---- it_fork_with_new_pty stdout ----
        thread 'it_fork_with_new_pty' panicked at 'assertion failed: child_tty != ""', tests/it_fork_with_new_pty.rs:31
stack backtrace:
   1:        0x105725758 - std::sys::imp::backtrace::tracing::imp::write::he3d1bfbdbf113480
   2:        0x105729a3f - std::panicking::default_hook::{{closure}}::h575f1b40d2e88f07
   3:        0x105728605 - std::panicking::default_hook::h3d5dccce8125d0cf
   4:        0x105728d36 - std::panicking::rust_panic_with_hook::h00b81bb3dcbd51f2
   5:        0x1056de423 - std::panicking::begin_panic::h70ee11343cda1bc2
   6:        0x1056e741c - it_fork_with_new_pty::it_fork_with_new_pty::hded79a5ea83bcc7c
   7:        0x1056f816e - <F as test::FnBox<T>>::call_box::h139af31b37861296
   8:        0x105729ffa - __rust_maybe_catch_panic
   9:        0x1056ed350 - std::panicking::try::do_call::he0c0a6db23f4cacc
  10:        0x105729ffa - __rust_maybe_catch_panic
  11:        0x1056f379a - <F as alloc::boxed::FnBox<A>>::call_box::hd0908040f09af183
  12:        0x105728144 - std::sys::imp::thread::Thread::new::thread_start::h990fb082eb5abe34
  13:     0x7fffdfe76aaa - _pthread_body
  14:     0x7fffdfe769f6 - _pthread_start

[hibariya]

Oops, I misunderstood about #8. This error occurs only on master and the PR fixes it.

[adjivas]

I have restart my check, unfortunately not, it's also a undefined behavior.