I tried looking around but couldn't reproduce this issue on my Ubuntu 14.04 vm
@ddunbar Any ideas?

Another failure spotted here: https://ci.swift.org/job/swift-PR-Linux/3867/console

I have looked into this a bit, since I was hitting it on Ubuntu 10.04. It only seems to happen when running the unit tests from `Utilities/bootstrap test`, not when just running the test from the command-line. I'm going to take another look at what the differences there are.

So, invoking `swift-test` in exactly the same manner as the bootstrap script does (`env SWIFT_EXEC=/home/user/swiftpm/.build/debug/swiftc SWIFT_BUILD_PATH=/home/user/swiftpm/.build /home/user/swiftpm/.build/debug/swift-test -Xlinker -rpath -Xlinker $ORIGIN/../lib/swift/linux`) does reproduce the problem. However, adding the test specifier flag (`-s UtilityTests.ShellTests`) doesn't trigger the bug. Only when running all the tests.

More data as I figure things out.

Also (perhaps unsurprisingly) the -Xlinker flags aren't relevant.

But removing all the tests except the `UtilityTests` does trigger the error.

Looks like the problem is with `ProgressBarTests`. If it runs before `ShellTests`, then the failure occurs. Otherwise not.

Oh of course: that code is messing with pseudo terminals etc.

Thanks @abertelrud for investigation, I was able to produce this locally after installing a fresh copy of Ubuntu
I have pushed a fix here #679

Fantastic. Thank you for the fix! We should try to get this into the next Swift bugfix release.