Add test-index-version

Commit 06aaaa0bf7 may step index format
version up and down, depends on whether extended flags present in the
index. This adds a test to check for index format version.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

.gitignore

@@ -153,6 +153,7 @@ test-date
 test-delta
 test-dump-cache-tree
 test-genrandom
+test-index-version
 test-match-trees
 test-parse-options
 test-path-utils

Makefile

@@ -1580,6 +1580,7 @@ TEST_PROGRAMS += test-parse-options$X
 TEST_PROGRAMS += test-path-utils$X
 TEST_PROGRAMS += test-sha1$X
 TEST_PROGRAMS += test-sigchain$X
+TEST_PROGRAMS += test-index-version$X
 
 all:: $(TEST_PROGRAMS)
 

test-index-version.c

@@ -0,0 +1,14 @@
+#include "cache.h"
+
+int main(int argc, const char **argv)
+{
+	struct cache_header hdr;
+	int version;
+
+	memset(&hdr,0,sizeof(hdr));
+	if (read(0, &hdr, sizeof(hdr)) != sizeof(hdr))
+		return 0;
+	version = ntohl(hdr.hdr_version);
+	printf("%d\n", version);
+	return 0;
+}