t7501-commit.sh: explicitly check that -F prevents invoking the editor

The "--signoff" test case in t7500-commit.sh was setting VISUAL while
using -F -, which indeed tested that the editor is not spawned with -F.
However, having it there was confusing, since there was no obvious reason
to the casual reader for it to be there.

This commits removes the setting of VISUAL from the --signoff test, and
adds in t7501-commit.sh a dedicated test case, where the rest of tests for
-F are.
Signed-off-by: NAdeodato Simó <dato@net.com.org.es>
Okay-then-by: NJohannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

t/t7500-commit.sh

@@ -149,10 +149,7 @@ EOF
 
 test_expect_success '--signoff' '
 	echo "yet another content *narf*" >> foo &&
-	echo "zort" | (
-		test_set_editor "$TEST_DIRECTORY"/t7500/add-content &&
-		git commit -s -F - foo
-	) &&
+	echo "zort" | git commit -s -F - foo &&
 	git cat-file commit HEAD | sed "1,/^$/d" > output &&
 	test_cmp expect output
 '

t/t7501-commit.sh

@@ -127,6 +127,26 @@ test_expect_success \
 	"showing committed revisions" \
 	"git rev-list HEAD >current"
 
+cat >editor <<\EOF
+#!/bin/sh
+sed -e "s/good/bad/g" < "$1" > "$1-"
+mv "$1-" "$1"
+EOF
+chmod 755 editor
+
+cat >msg <<EOF
+A good commit message.
+EOF
+
+test_expect_success \
+	'editor not invoked if -F is given' '
+	 echo "moo" >file &&
+	 VISUAL=./editor git commit -a -F msg &&
+	 git show -s --pretty=format:"%s" | grep -q good &&
+	 echo "quack" >file &&
+	 echo "Another good message." | VISUAL=./editor git commit -a -F - &&
+	 git show -s --pretty=format:"%s" | grep -q good
+	 '
 # We could just check the head sha1, but checking each commit makes it
 # easier to isolate bugs.