t7502: factor out autoident prerequisite

t7502 checks the behavior of commit when we can and cannot
determine a valid committer ident. Let's move that into
test-lib as a lazy prerequisite so other scripts can use it.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t7502-commit.sh

@@ -243,16 +243,6 @@ test_expect_success 'message shows author when it is not equal to committer' '
 	  .git/COMMIT_EDITMSG
 '
 
-test_expect_success 'setup auto-ident prerequisite' '
-	if (sane_unset GIT_COMMITTER_EMAIL &&
-	    sane_unset GIT_COMMITTER_NAME &&
-	    git var GIT_COMMITTER_IDENT); then
-		test_set_prereq AUTOIDENT
-	else
-		test_set_prereq NOAUTOIDENT
-	fi
-'
-
 test_expect_success AUTOIDENT 'message shows committer when it is automatic' '
 
 	echo >>negative &&
@@ -271,7 +261,7 @@ echo editor started > "$(pwd)/.git/result"
 exit 0
 EOF
 
-test_expect_success NOAUTOIDENT 'do not fire editor when committer is bogus' '
+test_expect_success !AUTOIDENT 'do not fire editor when committer is bogus' '
 	>.git/result
 	>expect &&
 

t/test-lib.sh

@@ -738,6 +738,12 @@ test_lazy_prereq UTF8_NFD_TO_NFC '
 	esac
 '
 
+test_lazy_prereq AUTOIDENT '
+	sane_unset GIT_AUTHOR_NAME &&
+	sane_unset GIT_AUTHOR_EMAIL &&
+	git var GIT_AUTHOR_IDENT
+'
+
 # When the tests are run as root, permission tests will report that
 # things are writable when they shouldn't be.
 test -w / || test_set_prereq SANITY