Optionally allow writing to stdout in test runs

[derekchiang]

Currently writes to stdout are redirected when running tests. However, in some cases it could be useful to allow writing to stdout. For instance, I was writing a wrapper for a C library and got a segment fault error. This caused my test to fail abruptly, as a result of which no useful output could be seen, since stdout was captured and the test wouldn't print the logs unless it failed normally.

I was able to get around this using std::io::stdio::stdout(), but that's not ideal.

[netvl]

I agree. Sometimes I write "interactive" tests which are intended to print something to the terminal. Previously it worked, and when I was porting old code to the new compiler, it surprised me that some tests became silent. This is a very useful feature sometimes. Probably add a flag to test binary?