diff: add tests for --relative without optional prefix value

We already have tests for --relative, but they currently only test when
a prefix has been provided. This fails to test the case where --relative
by itself should use the current directory as the prefix.

Teach the check_$type functions to take a directory argument to indicate
which subdirectory to run the git commands in. Add a new test which uses
this to test --relative without a prefix value.

Signed-off-by: Jacob Keller <jacob.keller@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4045-diff-relative.sh

@@ -13,6 +13,7 @@ test_expect_success 'setup' '
 '
 
 check_diff() {
+dir=$1; shift
 expect=$1; shift
 cat >expected <<EOF
 diff --git a/$expect b/$expect
@@ -24,50 +25,55 @@ index 0000000..25c05ef
 +other content
 EOF
 test_expect_success "-p $*" "
-	git diff -p $* HEAD^ >actual &&
+	git -C '$dir' diff -p $* HEAD^ >actual &&
 	test_cmp expected actual
 "
 }
 
 check_numstat() {
+dir=$1; shift
 expect=$1; shift
 cat >expected <<EOF
 1	0	$expect
 EOF
 test_expect_success "--numstat $*" "
 	echo '1	0	$expect' >expected &&
-	git diff --numstat $* HEAD^ >actual &&
+	git -C '$dir' diff --numstat $* HEAD^ >actual &&
 	test_cmp expected actual
 "
 }
 
 check_stat() {
+dir=$1; shift
 expect=$1; shift
 cat >expected <<EOF
  $expect | 1 +
  1 file changed, 1 insertion(+)
 EOF
 test_expect_success "--stat $*" "
-	git diff --stat $* HEAD^ >actual &&
+	git -C '$dir' diff --stat $* HEAD^ >actual &&
 	test_i18ncmp expected actual
 "
 }
 
 check_raw() {
+dir=$1; shift
 expect=$1; shift
 cat >expected <<EOF
 :000000 100644 0000000000000000000000000000000000000000 25c05ef3639d2d270e7fe765a67668f098092bc5 A	$expect
 EOF
 test_expect_success "--raw $*" "
-	git diff --no-abbrev --raw $* HEAD^ >actual &&
+	git -C '$dir' diff --no-abbrev --raw $* HEAD^ >actual &&
 	test_cmp expected actual
 "
 }
 
-for type in diff numstat stat raw; do
-	check_$type file2 --relative=subdir/
-	check_$type file2 --relative=subdir
-	check_$type dir/file2 --relative=sub
+for type in diff numstat stat raw
+do
+	check_$type . file2 --relative=subdir/
+	check_$type . file2 --relative=subdir
+	check_$type subdir file2 --relative
+	check_$type . dir/file2 --relative=sub
 done
 
 test_done