merge hook tests: fix and update tests

- update 'no editor' hook test and add 'editor' hook test
- make sure the tree is reset to a clean state after running a test
  (using test_when_finished) so later tests are not impacted

Signed-off-by: Benoit Pierre <benoit.pierre@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t7505-prepare-commit-msg-hook.sh

@@ -134,14 +134,26 @@ test_expect_success 'with hook (-c)' '
 
 test_expect_success 'with hook (merge)' '
 
-	head=`git rev-parse HEAD` &&
-	git checkout -b other HEAD@{1} &&
-	echo "more" >> file &&
+	test_when_finished "git checkout -f master" &&
+	git checkout -B other HEAD@{1} &&
+	echo "more" >>file &&
+	git add file &&
+	git commit -m other &&
+	git checkout - &&
+	git merge --no-ff other &&
+	test "`git log -1 --pretty=format:%s`" = "merge (no editor)"
+'
+
+test_expect_success 'with hook and editor (merge)' '
+
+	test_when_finished "git checkout -f master" &&
+	git checkout -B other HEAD@{1} &&
+	echo "more" >>file &&
 	git add file &&
 	git commit -m other &&
 	git checkout - &&
-	git merge other &&
-	test "`git log -1 --pretty=format:%s`" = merge
+	env GIT_EDITOR="\"\$FAKE_EDITOR\"" git merge --no-ff -e other &&
+	test "`git log -1 --pretty=format:%s`" = "merge"
 '
 
 cat > "$HOOK" <<'EOF'
@@ -151,6 +163,7 @@ EOF
 
 test_expect_success 'with failing hook' '
 
+	test_when_finished "git checkout -f master" &&
 	head=`git rev-parse HEAD` &&
 	echo "more" >> file &&
 	git add file &&
@@ -160,6 +173,7 @@ test_expect_success 'with failing hook' '
 
 test_expect_success 'with failing hook (--no-verify)' '
 
+	test_when_finished "git checkout -f master" &&
 	head=`git rev-parse HEAD` &&
 	echo "more" >> file &&
 	git add file &&
@@ -169,6 +183,7 @@ test_expect_success 'with failing hook (--no-verify)' '
 
 test_expect_success 'with failing hook (merge)' '
 
+	test_when_finished "git checkout -f master" &&
 	git checkout -B other HEAD@{1} &&
 	echo "more" >> file &&
 	git add file &&
@@ -178,7 +193,7 @@ test_expect_success 'with failing hook (merge)' '
 	exit 1
 	EOF
 	git checkout - &&
-	test_must_fail git merge other
+	test_must_fail git merge --no-ff other
 
 '