[FIX] mail: allow to preview a template in a specific lang

Followup of odoo/odoo@2d6df1fe7a : when forcing language in template preview
result is not returned according to the expected format.

Add tests.

Task-2643750

closes odoo/odoo#76458

X-original-commit: 80c6001f6f46cc548fb4e337ba71908bea768d86
Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>
Co-authored-by: Thibault Delavallee <tde@odoo.com>

addons/mail/models/mail_render_mixin.py

@@ -498,11 +498,11 @@ class MailRenderMixin(models.AbstractModel):
         self.ensure_one()
 
         if self.env.context.get('template_preview_lang'):
-            return dict((res_id, self.env.context['template_preview_lang']) for res_id in res_ids)
-
-        lang_to_res_ids = {}
-        for res_id, lang in self._render_lang(res_ids, engine=engine).items():
-            lang_to_res_ids.setdefault(lang, []).append(res_id)
+            lang_to_res_ids = {self.env.context['template_preview_lang']: res_ids}
+        else:
+            lang_to_res_ids = {}
+            for res_id, lang in self._render_lang(res_ids, engine=engine).items():
+                lang_to_res_ids.setdefault(lang, []).append(res_id)
 
         return dict(
             (lang, (self.with_context(lang=lang) if lang else self, lang_res_ids))

addons/test_mail/tests/__init__.py

@@ -11,6 +11,7 @@ from . import test_mail_mail
 from . import test_mail_gateway
 from . import test_mail_thread_internals
 from . import test_mail_template
+from . import test_mail_template_preview
 from . import test_message_management
 from . import test_message_post
 from . import test_message_track

addons/test_mail/tests/test_mail_template_preview.py

@@ -0,0 +1,26 @@
+# -*- coding: utf-8 -*-
+# Part of Odoo. See LICENSE file for full copyright and licensing details.
+
+from odoo.addons.test_mail.tests.test_mail_template import TestMailTemplate
+from odoo.tests import tagged
+
+
+@tagged('mail_template')
+class TestMailTemplateTools(TestMailTemplate):
+
+    def test_mail_template_preview_force_lang(self):
+        test_record = self.env['mail.test.lang'].browse(self.test_record.ids)
+        test_record.write({
+            'lang': 'es_ES',
+        })
+        test_template = self.env['mail.template'].browse(self.test_template.ids)
+
+        preview = self.env['mail.template.preview'].create({
+            'mail_template_id': test_template.id,
+            'resource_ref': test_record,
+            'lang': 'es_ES',
+        })
+        self.assertEqual(preview.body_html, '<p>Spanish Body for %s</p>' % test_record.name)
+
+        preview.write({'lang': 'en_US'})
+        self.assertEqual(preview.body_html, '<p>English Body for %s</p>' % test_record.name)