Add tests for git-prune

It seems that git prune changed behaviour with respect to revisions added
from command line, probably when it became a builtin. Currently, it prints
a short usage and exits: instead, it should take those revisions into
account and not prune them. So add a couple of test to point this out.

We'll be fixing this by switching to parse_options(), so add tests to
detect bogus command line parameters as well, to keep ourselves from
introducing regressions.

Signed-off-by: Michele Ballabio <barra_cuda@katamail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t5304-prune.sh

@@ -78,4 +78,38 @@ test_expect_success 'gc: start with ok gc.pruneExpire' '
 
 '
 
+test_expect_success 'prune: prune nonsense parameters' '
+
+	test_must_fail git prune garbage &&
+	test_must_fail git prune --- &&
+	test_must_fail git prune --no-such-option
+
+'
+
+test_expect_success 'prune: prune unreachable heads' '
+
+	git config core.logAllRefUpdates false &&
+	mv .git/logs .git/logs.old &&
+	: > file2 &&
+	git add file2 &&
+	git commit -m temporary &&
+	tmp_head=$(git rev-list -1 HEAD) &&
+	git reset HEAD^ &&
+	git prune &&
+	test_must_fail git reset $tmp_head --
+
+'
+
+test_expect_failure 'prune: do not prune heads listed as an argument' '
+
+	: > file2 &&
+	git add file2 &&
+	git commit -m temporary &&
+	tmp_head=$(git rev-list -1 HEAD) &&
+	git reset HEAD^ &&
+	git prune -- $tmp_head &&
+	git reset $tmp_head --
+
+'
+
 test_done