git-notes: Run partial expensive test everywhere

The git-notes expensive timing test is only expensive because it
either did 10,100,1k and 10k iterations or nothing.

Change it to do 10 by default, with an option to run the expensive
version with the old GIT_NOTES_TIMING_TESTS=ZomgYesPlease variable.

Since nobody was ostensibly running this test under TAP the code had
bitrotted so that it emitted invalid TAP. This change fixes that.

The old version would also mysteriously fail on systems without
/usr/bin/time, there's now a check for that using the multiple test
prerequisite facility.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t3302-notes-index-expensive.sh

@@ -7,11 +7,9 @@ test_description='Test commit notes index (expensive!)'
 
 . ./test-lib.sh
 
-test -z "$GIT_NOTES_TIMING_TESTS" && {
-	skip_all="Skipping timing tests"
-	test_done
-	exit
-}
+test_set_prereq NOT_EXPENSIVE
+test -n "$GIT_NOTES_TIMING_TESTS" && test_set_prereq EXPENSIVE
+test -x /usr/bin/time && test_set_prereq USR_BIN_TIME
 
 create_repo () {
 	number_of_commits=$1
@@ -102,17 +100,27 @@ time_notes () {
 	done
 }
 
-for count in 10 100 1000 10000; do
+do_tests () {
+	pr=$1
+	count=$2
+
+	test_expect_success $pr 'setup / mkdir' '
+		mkdir $count &&
+		cd $count
+	'
 
-	mkdir $count
-	(cd $count;
+	test_expect_success $pr "setup $count" "create_repo $count"
 
-	test_expect_success "setup $count" "create_repo $count"
+	test_expect_success $pr 'notes work' "test_notes $count"
 
-	test_expect_success 'notes work' "test_notes $count"
+	test_expect_success USR_BIN_TIME,$pr 'notes timing with /usr/bin/time' "time_notes 100"
+
+	test_expect_success $pr 'teardown / cd ..' 'cd ..'
+}
 
-	test_expect_success 'notes timing' "time_notes 100"
-	)
+do_tests NOT_EXPENSIVE 10
+for count in 100 1000 10000; do
+	do_tests EXPENSIVE $count
 done
 
 test_done