Test output to a TTY.
summer will auto-detect if stdout is a tty or not, and change some of the
output accordingly. In this test framework, stdout is not a TTY, so all other
tests use that codepath.
In this test we force tty output, and check the output is as expected.
$ alias summer="$TESTDIR/../summer"
$ touch file1 file2 file3
$ summer -forcetty -n generate .
\r (no-eol) (esc)
0s: 0 matched, 0 modified, 3 new, 0 corrupted