p7300: add performance tests for clean

The tests are run in dry-run mode to avoid having to restore the test
directories for each timed iteration. Using dry-run is an acceptable
compromise since we are mostly interested in the initial computation
of what to clean and not so much in the cleaning it self.

Signed-off-by: Erik Elfström <erik.elfstrom@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/perf/p7300-clean.sh

@@ -0,0 +1,31 @@
+#!/bin/sh
+
+test_description="Test git-clean performance"
+
+. ./perf-lib.sh
+
+test_perf_default_repo
+test_checkout_worktree
+
+test_expect_success 'setup untracked directory with many sub dirs' '
+	rm -rf 500_sub_dirs 100000_sub_dirs clean_test_dir &&
+	mkdir 500_sub_dirs 100000_sub_dirs clean_test_dir &&
+	for i in $(test_seq 1 500)
+	do
+		mkdir 500_sub_dirs/dir$i || return $?
+	done &&
+	for i in $(test_seq 1 200)
+	do
+		cp -r 500_sub_dirs 100000_sub_dirs/dir$i || return $?
+	done
+'
+
+test_perf 'clean many untracked sub dirs, check for nested git' '
+	git clean -n -q -f -d 100000_sub_dirs/
+'
+
+test_perf 'clean many untracked sub dirs, ignore nested git' '
+	git clean -n -q -f -f -d 100000_sub_dirs/
+'
+
+test_done