Unlessptytest output is consumed, a test can hang if a command outputs more than1024 bytes (at least on macOS).

There are two ways to work around this issue:

1. Consume the output viapty.ExpectMatch() (ensure no more than 1024 bytes are left unread)
2. Usecmd.SetOut(io.Discard) instead

Since usingptytest is a common pattern in our tests, it'd be a good idea to rewrite it so that a hang is not possible.

Unless there's a bug to be fixed in underlying libraries, or changes to how ptys are configured, the most robust way to fix this would be forptytest to buffer/consumeall command output, irregardless of a call toExpectMatch.

A reproduction of this bug exists as a test in#1629 (and will be merged in and skipped on macOS and Windows).