t4200: prefer help-functions to "test -(d|f)"

The original code works fine. However, The code base has already had help-functions(in test-lib-functions),
"test -d" and "test -f" are replaced with "test_path_is_dir" and "test_path_is_file" respectively in this commit because
they are more friendly to debug.

* t4200-rerere.sh: replace "test -d" with "test_path_is_dir"
* t4200-rerere.sh: replace "test -f" with "test_path_is_file"

Signed-off-by: Angel Pan <dinoallosaurus1111@gmail.com>

t/t4200-rerere.sh

@@ -70,7 +70,7 @@ test_expect_success 'nothing recorded without rerere' '
 	rm -rf .git/rr-cache &&
 	git config rerere.enabled false &&
 	test_must_fail git merge first &&
-	! test -d .git/rr-cache
+	! test_path_is_dir .git/rr-cache
 '
 
 test_expect_success 'activate rerere, old style (conflicting merge)' '
@@ -82,8 +82,8 @@ test_expect_success 'activate rerere, old style (conflicting merge)' '
 	sha1=$(perl -pe "s/	.*//" .git/MERGE_RR) &&
 	rr=.git/rr-cache/$sha1 &&
 	grep "^=======\$" $rr/preimage &&
-	! test -f $rr/postimage &&
-	! test -f $rr/thisimage
+	! test_path_is_file $rr/postimage &&
+	! test_path_is_file $rr/thisimage
 '
 
 test_expect_success 'rerere.enabled works, too' '
@@ -108,8 +108,8 @@ test_expect_success 'set up rr-cache' '
 
 test_expect_success 'rr-cache looks sane' '
 	# no postimage or thisimage yet
-	! test -f $rr/postimage &&
-	! test -f $rr/thisimage &&
+	! test_path_is_file $rr/postimage &&
+	! test_path_is_file $rr/thisimage &&
 
 	# preimage has right number of lines
 	cnt=$(sed -ne "/^<<<<<<</,/^>>>>>>>/p" $rr/preimage | wc -l) &&
@@ -165,7 +165,7 @@ test_expect_success 'first postimage wins' '
 	git show first:a1 | sed "s/To die: t/To die! T/" >expect &&
 
 	git commit -q -a -m "prefer first over second" &&
-	test -f $rr/postimage &&
+	test_path_is_file $rr/postimage &&
 
 	oldmtimepost=$(test-tool chmtime --get -60 $rr/postimage) &&
 
@@ -188,22 +188,22 @@ test_expect_success 'rerere clear' '
 	mv $rr/postimage .git/post-saved &&
 	echo "$sha1	a1" | perl -pe "y/\012/\000/" >.git/MERGE_RR &&
 	git rerere clear &&
-	! test -d $rr
+	! test_path_is_dir $rr
 '
 
 test_expect_success 'leftover directory' '
 	git reset --hard &&
 	mkdir -p $rr &&
 	test_must_fail git merge first &&
-	test -f $rr/preimage
+	test_path_is_file $rr/preimage
 '
 
 test_expect_success 'missing preimage' '
 	git reset --hard &&
 	mkdir -p $rr &&
 	cp .git/post-saved $rr/postimage &&
 	test_must_fail git merge first &&
-	test -f $rr/preimage
+	test_path_is_file $rr/preimage
 '
 
 test_expect_success 'set up for garbage collection tests' '
@@ -228,16 +228,16 @@ test_expect_success 'set up for garbage collection tests' '
 
 test_expect_success 'gc preserves young or recently used records' '
 	git rerere gc &&
-	test -f $rr/preimage &&
-	test -f $rr2/preimage
+	test_path_is_file $rr/preimage &&
+	test_path_is_file $rr2/preimage
 '
 
 test_expect_success 'old records rest in peace' '
 	test-tool chmtime =$just_over_60_days_ago $rr/postimage &&
 	test-tool chmtime =$just_over_15_days_ago $rr2/preimage &&
 	git rerere gc &&
-	! test -f $rr/preimage &&
-	! test -f $rr2/preimage
+	! test_path_is_file $rr/preimage &&
+	! test_path_is_file $rr2/preimage
 '
 
 rerere_gc_custom_expiry_test () {