test/parallel: add a test for negative jobs number arguments

Before commit 48b0d26, -j2 and -j -2 both triggered an infinite
loop. That commit fixed the infinite loop but -j2 and -j -2 are still
parsed the same. In the corresponding code review bats-core#657 Martin expressed
an intent to change the parser and parse these differently in the
future.

In commit 0ec3619 Martin added a "no infinite loop" test for
"-j2". However this test will stop testing negative arguments when the
parser changes (the test will also have to be adjusted when the parser
changes).

Add one additional test with a "-j -3" argument that will test a
negative argument forever.

Signed-off-by: Marc Herbert <marc.herbert@intel.com>

test/parallel.bats

@@ -218,3 +218,10 @@ check_parallel_tests() { # <expected maximum parallelity>
   (( SECONDS < 5 ))
   [ "${lines[1]}" = 'Invalid number of jobs: -2' ]
 }
+
+@test "Negative jobs number does not run endlessly" {
+  unset BATS_NO_PARALLELIZE_ACROSS_FILES
+  run bats -j -3 "$FIXTURE_ROOT/../bats/passing.bats"
+  (( SECONDS < 5 ))
+  [ "${lines[1]}" = 'Invalid number of jobs: -3' ]
+}