mktag tests: improve verify_object() test coverage

The verify_object() function in "mktag.c" is tasked with ensuring that
our tag refers to a valid object.

The existing test for this might fail because it was also testing that
"type taggg" didn't refer to a valid object type (it should be "type
tag"), or because we referred to a valid object but got the type
wrong.

Let's split these tests up, so we're testing all combinations of a
non-existing object and in invalid/wrong "type" lines.

We need to provide GIT_TEST_GETTEXT_POISON=false here because the
"invalid object type" error is emitted by
parse_loose_header_extended(), which has that message already marked
for translation. Another option would be to use test_i18ngrep, but I
prefer always running the test, not skipping it under gettext poison
testing.

I'm not testing this in combination with "git replace". That'll be
done in a subsequent commit.

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

t/t3800-mktag.sh

@@ -14,7 +14,8 @@ test_description='git mktag: tag object verify test'
 check_verify_failure () {
 	expect="$2"
 	test_expect_success "$1" '
-		test_must_fail git mktag <tag.sig 2>message &&
+		test_must_fail env GIT_TEST_GETTEXT_POISON=false \
+			git mktag <tag.sig 2>message &&
 		grep "$expect" message
 	'
 }
@@ -136,7 +137,29 @@ check_verify_failure '"type" line type-name length check' \
 	'^error: char.*: type too long$'
 
 ############################################################
-#  9. verify object (SHA1/type) check
+#  9. verify object (hash/type) check
+
+cat >tag.sig <<EOF
+object $(test_oid deadbeef)
+type tag
+tag mytag
+tagger . <> 0 +0000
+
+EOF
+
+check_verify_failure 'verify object (hash/type) check -- correct type, nonexisting object' \
+	'^error: char7: could not verify object.*$'
+
+cat >tag.sig <<EOF
+object $head
+type tagggg
+tag mytag
+tagger . <> 0 +0000
+
+EOF
+
+check_verify_failure 'verify object (hash/type) check -- made-up type, valid object' \
+	'^fatal: invalid object type'
 
 cat >tag.sig <<EOF
 object $(test_oid deadbeef)
@@ -146,9 +169,20 @@ tagger . <> 0 +0000
 
 EOF
 
-check_verify_failure 'verify object (SHA1/type) check' \
+check_verify_failure 'verify object (hash/type) check -- made-up type, nonexisting object' \
 	'^error: char7: could not verify object.*$'
 
+cat >tag.sig <<EOF
+object $head
+type tree
+tag mytag
+tagger . <> 0 +0000
+
+EOF
+
+check_verify_failure 'verify object (hash/type) check -- mismatched type, valid object' \
+	'^error: char7: could not verify object'
+
 ############################################################
 # 10. verify tag-name check