t3200: verify "branch --list" sanity when rebasing from detached HEAD

"git branch --list" shows an in-progress rebase as:

  * (no branch, rebasing <branch>)
    master
    ...

However, if the rebase is started from a detached HEAD, then there is no
<branch>, and it would attempt to print a NULL pointer. The previous
commit fixed this problem, so add a test to verify that the output is
sane in this situation.

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Kaartic Sivaraam <kaartic.sivaraam@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t3200-branch.sh

@@ -6,6 +6,7 @@
 test_description='git branch assorted tests'
 
 . ./test-lib.sh
+. "$TEST_DIRECTORY"/lib-rebase.sh
 
 test_expect_success 'prepare a trivial repository' '
 	echo Hello >A &&
@@ -1246,6 +1247,29 @@ test_expect_success '--merged is incompatible with --no-merged' '
 	test_must_fail git branch --merged HEAD --no-merged HEAD
 '
 
+test_expect_success '--list during rebase' '
+	test_when_finished "reset_rebase" &&
+	git checkout master &&
+	FAKE_LINES="1 edit 2" &&
+	export FAKE_LINES &&
+	set_fake_editor &&
+	git rebase -i HEAD~2 &&
+	git branch --list >actual &&
+	test_i18ngrep "rebasing master" actual
+'
+
+test_expect_success '--list during rebase from detached HEAD' '
+	test_when_finished "reset_rebase && git checkout master" &&
+	git checkout master^0 &&
+	oid=$(git rev-parse --short HEAD) &&
+	FAKE_LINES="1 edit 2" &&
+	export FAKE_LINES &&
+	set_fake_editor &&
+	git rebase -i HEAD~2 &&
+	git branch --list >actual &&
+	test_i18ngrep "rebasing detached HEAD $oid" actual
+'
+
 test_expect_success 'tracking with unexpected .fetch refspec' '
 	rm -rf a b c d &&
 	git init a &&