Convert `[]` to `test` and break if-then into separate lines, both of
which bring the style in line with Git's coding guidelines.

Signed-off-by: Denton Liu <redacted>
---
 t/t2018-checkout-branch.sh | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/t/t2018-checkout-branch.sh b/t/t2018-checkout-branch.sh
index 79b16e4677..61206a90fb 100755
--- a/t/t2018-checkout-branch.sh
+++ b/t/t2018-checkout-branch.sh

@@ -20,7 +20,8 @@ do_checkout () {
 	exp_sha=${2:-$(git rev-parse --verify HEAD)} &&
 
 	# default options for git checkout: -b
-	if [ -z "$3" ]; then
+	if test -z "$3"
+	then
 		opts="-b"
 	else
 		opts="$3"

-- 
2.25.0.rc1.180.g49a268d3eb