test for add with non-existent pathspec

Add a test for 'git add -u pathspec' and 'git add pathspec' where
pathspec does not exist. The expected result is that git add exits with
an error message and an appropriate exit code.

Signed-off-by: Chris Packham <judge.packham@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t2200-add-update.sh

@@ -176,4 +176,9 @@ test_expect_success 'add -u resolves unmerged paths' '
 
 '
 
+test_expect_success '"add -u non-existent" should fail' '
+	test_must_fail git add -u non-existent &&
+	! (git ls-files | grep "non-existent")
+'
+
 test_done

t/t3700-add.sh

@@ -255,4 +255,9 @@ test_expect_success 'git add to resolve conflicts on otherwise ignored path' '
 	git add track-this
 '
 
+test_expect_success '"add non-existent" should fail' '
+	test_must_fail git add non-existent &&
+	! (git ls-files | grep "non-existent")
+'
+
 test_done