tests: check --[short]stat output after chmod

Add a test to check 'diff --stat' output with a text file after chmod,
and the same for a binary file. This demonstrates that text and binary
files are treated differently, which can be misleading.

While at it, add tests to check --shortstat output, too.

Reported-by: Martin Mareš <mj@ucw.cz>
Signed-off-by: Zbigniew Jędrzejewski-Szmek <zbyszek@in.waw.pl>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4006-diff-mode.sh

@@ -25,4 +25,41 @@ test_expect_success 'chmod' '
 	test_cmp expected check
 '
 
+test_expect_success 'prepare binary file' '
+	git commit -m rezrov &&
+	dd if=/dev/zero of=binbin bs=1024 count=1 &&
+	git add binbin &&
+	git commit -m binbin
+'
+
+test_expect_success '--stat output after text chmod' '
+	test_chmod -x rezrov &&
+	echo " 0 files changed" >expect &&
+	git diff HEAD --stat >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success '--shortstat output after text chmod' '
+	git diff HEAD --shortstat >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success '--stat output after binary chmod' '
+	test_chmod +x binbin &&
+	cat >expect <<-EOF &&
+	 binbin |  Bin 1024 -> 1024 bytes
+	 1 file changed, 0 insertions(+), 0 deletions(-)
+	EOF
+	git diff HEAD --stat >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success '--shortstat output after binary chmod' '
+	cat >expect <<-EOF &&
+	 1 file changed, 0 insertions(+), 0 deletions(-)
+	EOF
+	git diff HEAD --shortstat >actual &&
+	test_cmp expect actual
+'
+
 test_done