[PATCH 23/30] t1409: test with packed-refs v2

["Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com>]

From: Derrick Stolee <derrickstolee@github.com>

t1409-avoid-packing-refs.sh seeks to test that the packed-refs file is
not modified unnecessarily. One way it does this is by creating a
packed-refs file, then munging its contents and verifying that the
munged data remains after other commands.

For packed-refs v1, it suffices to add a line that is similar to a
comment. For packed-refs v2, we cannot even add to the file without
messing up the trailing table of contents of its chunked format.
However, we can manipulate the last bytes that are within the trailing
hash and use 'tail -c 4' to read them.

This makes t1409 pass with GIT_TEST_PACKED_REFS_VERSION=2.

Signed-off-by: Derrick Stolee <derrickstolee@github.com>
---
 t/t1409-avoid-packing-refs.sh | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/t/t1409-avoid-packing-refs.sh b/t/t1409-avoid-packing-refs.sh
index be12fb63506..dc8d58432c8 100755
--- a/t/t1409-avoid-packing-refs.sh
+++ b/t/t1409-avoid-packing-refs.sh
@@ -8,13 +8,29 @@ test_description='avoid rewriting packed-refs unnecessarily'
 # shouldn't upset readers, and it should be omitted if the file is
 # ever rewritten.
 mark_packed_refs () {
-	sed -e "s/^\(#.*\)/\1 t1409 /" .git/packed-refs >.git/packed-refs.new &&
-	mv .git/packed-refs.new .git/packed-refs
+	if test "$GIT_TEST_PACKED_REFS_VERSION" = "2"
+	then
+		size=$(wc -c < .git/packed-refs) &&
+		pos=$(expr $size - 4) &&
+		printf "FAKE" | dd of=".git/packed-refs" bs=1 seek="$pos" conv=notrunc
+	else
+		sed -e "s/^\(#.*\)/\1 t1409 /" .git/packed-refs >.git/packed-refs.new &&
+		mv .git/packed-refs.new .git/packed-refs
+	fi
 }
 
 # Verify that the packed-refs file is still marked.
 check_packed_refs_marked () {
-	grep -q '^#.* t1409 ' .git/packed-refs
+	if test "$GIT_TEST_PACKED_REFS_VERSION" = "2"
+	then
+		size=$(wc -c < .git/packed-refs) &&
+		pos=$(expr $size - 4) &&
+		tail -c 4 .git/packed-refs >actual &&
+		printf "FAKE" >expect &&
+		test_cmp expect actual
+	else
+		grep -q '^#.* t1409 ' .git/packed-refs
+	fi
 }
 
 test_expect_success 'setup' '
-- 
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