t: detect errors outside of test cases

We have recently merged a patch series that had a simple misspelling of
`test_expect_success`. Instead of making our tests fail though, this
typo went completely undetected and all of our tests passed, which is of
course unfortunate. This is a more general issue with our test suite:
all commands that run outside of a specific test case can fail, and if
we don't explicitly check for such failure then this failure will be
silently ignored.

Improve the status quo by enabling the errexit option so that any such
unchecked failures will cause us to abort immediately.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: pks-t

t/test-lib.sh

@@ -15,6 +15,10 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see https://www.gnu.org/licenses/ .
 
+# Enable the use of errexit so that any unexpected failures will cause us to
+# abort tests, even when outside of a specific test case.
+set -e
+
 # Test the binaries we have just built.  The tests are kept in
 # t/ subdirectory and are run in 'trash directory' subdirectory.
 if test -z "$TEST_DIRECTORY"