t9811: replace 'test -f' and '! test -f' with 'test_path_*'

Replace the basic shell commands 'test -f', with more modern test
helpers 'test_path_is_file' and 'test_path_is_missing'.
These modern helpers emit useful information when the corresponding
tests fail, unlike 'test -f' and '! test -f'.

The occurrences of '! test -f filename' were replaced by
'file_path_is_missing filename', a stronger guarantee equivalent to
'! test -e filename'.

Co-authored-by: Vinicius Lira de Freitas <vinilira@usp.br>
Signed-off-by: Vinicius Lira de Freitas <vinilira@usp.br>
Signed-off-by: Marcelo Machado Lage <marcelomlage@usp.br>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t9811-git-p4-label-import.sh

diff --git a/t/t9811-git-p4-label-import.sh b/t/t9811-git-p4-label-import.sh
index 9c16103..ee25701 100755
--- a/t/t9811-git-p4-label-import.sh
+++ b/t/t9811-git-p4-label-import.sh
@@ -62,11 +62,11 @@
 
 		cd main &&
 		git checkout TAG_F1_ONLY &&
-		! test -f f2 &&
+		test_path_is_missing f2 &&
 		git checkout TAG_WITH\$_SHELL_CHAR &&
-		test -f f1 &&
-		test -f f2 &&
-		test -f file_with_\$metachar &&
+		test_path_is_file f1 &&
+		test_path_is_file f2 &&
+		test_path_is_file file_with_\$metachar &&
 
 		git show TAG_LONG_LABEL | grep -q "A Label second line"
 	)
@@ -104,11 +104,11 @@
 
 		git checkout TAG_F1_1 &&
 		ls &&
-		test -f f1 &&
+		test_path_is_file f1 &&
 
 		git checkout TAG_F1_2 &&
 		ls &&
-		test -f f1
+		test_path_is_file f1
 	)
 '
 
@@ -137,9 +137,9 @@
 		p4 labels ... | grep LIGHTWEIGHT_TAG &&
 		p4 label -o GIT_TAG_1 | grep "tag created in git:xyzzy" &&
 		p4 sync ...@GIT_TAG_1 &&
-		! test -f main/f10 &&
+		test_path_is_missing main/f10 &&
 		p4 sync ...@GIT_TAG_2 &&
-		test -f main/f10
+		test_path_is_file main/f10
 	)
 '
 
@@ -170,9 +170,9 @@
 		cd "$cli" &&
 		p4 sync ... &&
 		p4 sync ...@GIT_TAG_ON_DELETED &&
-		test -f main/deleted_file &&
+		test_path_is_file main/deleted_file &&
 		p4 sync ...@GIT_TAG_AFTER_DELETION &&
-		! test -f main/deleted_file &&
+		test_path_is_missing main/deleted_file &&
 		echo "checking label contents" &&
 		p4 label -o GIT_TAG_ON_DELETED | grep "tag on deleted file"
 	)