[PATCH] t6002: make test "set -e" clean

[Junio C Hamano <gitster@pobox.com>]

In order to catch mistakes like misspelling "test_expect_success",
we would like to eventually be able to run our test suite with the
"-e" option on.

We often use 

      val=$(expr expression)

only for the computation, and it is good that "expr" exits non-zero
with syntactically invalid expression (it exits with 2) and other
errors (with 3).

"expr" however also exits with "1" if it yields 0 or null X-<.

Make sure we do not fail unnecessarily under "set -e".

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---

 * It was fun to figure this one out.

 t/t6002-rev-list-bisect.sh | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git i/t/t6002-rev-list-bisect.sh w/t/t6002-rev-list-bisect.sh
index daa009c9a1..1bd720d240 100755
--- i/t/t6002-rev-list-bisect.sh
+++ w/t/t6002-rev-list-bisect.sh
@@ -27,9 +27,9 @@ test_bisection_diff()
 	# Test if bisection size is close to half of list size within
 	# tolerance.
 	#
-	_bisect_err=$(expr $_list_size - $_bisection_size \* 2)
+	_bisect_err=$(expr $_list_size - $_bisection_size \* 2) && test $? -le 1
 	test "$_bisect_err" -lt 0 && _bisect_err=$(expr 0 - $_bisect_err)
-	_bisect_err=$(expr $_bisect_err / 2) ; # floor
+	_bisect_err=$(expr $_bisect_err / 2) && test $? -le 1; # floor
 
 	test_expect_success \
 	"bisection diff $_bisect_option $_head $* <= $_max_diff" \