From: Roger Koranteng <rogerkorantenng@gmail.com>

The only "mktree --batch" test in t1010 is the one checking that it
survives a concurrent repack. Nothing covers basic batch mode, which
is how the leak fixed in 6272f3bd17 (mktree: plug per-tree leak in
--batch mode, 2026-08-29) went unnoticed.

Add a few tests for it. Two trees in one batch should get the same
IDs as running plain "mktree" on each, a trailing blank line should
not add an extra tree, -z input should work, and a tree that names a
missing object should make mktree die after printing the trees before
it. While at it, check that a blank line is rejected without --batch.

One test feeds two blank lines in a row and expects an empty tree in
between. That is what mktree does today, but the documentation says
trees are separated by "a single blank line", so I am not sure it is
intended. The test records the current behaviour.

Suggested-by: Jeff King <peff@peff.net>
Signed-off-by: Roger Koranteng <rogerkorantenng@gmail.com>

Submitted-As: https://lore.kernel.org/git/pull.2270.git.1792497283164.gitgitgadget@gmail.com