show tests: add test for "git show <tree>"

Add missing tests for showing a tree with "git show". Let's test for
showing a tree, two trees, and that doing so doesn't recurse.

The only tests for this code added in 5d7eeee (git-show: grok
blobs, trees and tags, too, 2006-12-14) were the tests in
t7701-repack-unpack-unreachable.sh added in ccc1297 (repack:
modify behavior of -A option to leave unreferenced objects unpacked,
2008-05-09).

Let's add this common mode of operation to the "show" tests
themselves. It's more obvious, and the tests in
t7701-repack-unpack-unreachable.sh happily pass if we start buggily
emitting trees recursively.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t7007-show.sh

@@ -38,6 +38,45 @@ test_expect_success 'showing two commits' '
 	test_cmp expect actual.filtered
 '
 
+test_expect_success 'showing a tree' '
+	cat >expected <<-EOF &&
+	tree main1:
+
+	main1.t
+	EOF
+	git show main1: >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'showing two trees' '
+	cat >expected <<-EOF &&
+	tree main1^{tree}
+
+	main1.t
+
+	tree main2^{tree}
+
+	main1.t
+	main2.t
+	EOF
+	git show main1^{tree} main2^{tree} >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'showing a trees is not recursive' '
+	git worktree add not-recursive main1 &&
+	mkdir not-recursive/a &&
+	test_commit -C not-recursive a/file &&
+	cat >expected <<-EOF &&
+	tree HEAD^{tree}
+
+	a/
+	main1.t
+	EOF
+	git -C not-recursive show HEAD^{tree} >actual &&
+	test_cmp expected actual
+'
+
 test_expect_success 'showing a range walks (linear)' '
 	cat >expect <<-EOF &&
 	commit $(git rev-parse main3)