diff --git a/cms_form/tests/common.py b/cms_form/tests/common.py
index 08e613ec..b2126e47 100644
--- a/cms_form/tests/common.py
+++ b/cms_form/tests/common.py
@@ -4,7 +4,7 @@
 from lxml import html
 from odoo_test_helper import FakeModelLoader
 
-from odoo.tests.common import HttpCase, TransactionCase
+from odoo.tests.common import HttpCase, TransactionCase, tagged
 
 from .utils import fake_request, fake_session, session_store
 
@@ -79,12 +79,10 @@ def assert_match_inputs(self, node, expected):
             self.assertEqual(len(self.find_input_name(node, name)), 1)
 
 
+@tagged("post_install", "-at_install")
 class FormTestCase(TransactionCase, FakeModelMixin):
     """Form test cases."""
 
-    at_install = False
-    post_install = True
-
     @classmethod
     def setUpClass(cls):
         super().setUpClass()
@@ -115,6 +113,7 @@ class FormRenderTestCase(FormTestCase, HTMLRenderMixin):
     """Form test cases where you test HTML rendering."""
 
 
+@tagged("post_install", "-at_install")
 class FormHttpTestCase(HttpCase, FakeModelMixin, HTMLRenderMixin):
     """Form test cases where you test HTML rendering and HTTP requests."""
 
diff --git a/cms_form/tests/fake_models/fake_fields_form.py b/cms_form/tests/fake_models/fake_fields_form.py
index 4f90be4a..1df280f4 100644
--- a/cms_form/tests/fake_models/fake_fields_form.py
+++ b/cms_form/tests/fake_models/fake_fields_form.py
@@ -8,6 +8,7 @@ class FakeFloatWidget(models.AbstractModel):
 
     _name = "cms.form.test_fields.widget.float"
     _inherit = "cms.form.widget.float"
+    _description = _name
 
 
 class FakeFieldsForm(models.AbstractModel):
@@ -51,6 +52,7 @@ class FakeFieldsForm2(models.AbstractModel):
 
     _name = "cms.form.test_fields2"
     _inherit = "cms.form.test_fields"
+    _description = _name
 
     a_float_with_another_widget = fields.Float(
         form_widget={"model": FakeFloatWidget._name}
diff --git a/cms_form/tests/test_controllers.py b/cms_form/tests/test_controllers.py
index 7e7acfe2..5b52206b 100644
--- a/cms_form/tests/test_controllers.py
+++ b/cms_form/tests/test_controllers.py
@@ -5,6 +5,8 @@
 import os
 import unittest
 
+from odoo.addons.website.tools import MockRequest
+
 from ..controllers import main
 from .common import FormHttpTestCase, FormTestCase
 from .utils import fake_request, mock_request
@@ -26,6 +28,8 @@ def setUp(self):
         self.form_controller = main.CMSFormController()
         self.form_search_controller = main.CMSSearchFormController()
         self.form_wiz_controller = main.CMSWizardFormController()
+        # do not rely on demo data (eg: `base.res_partner_12`) being loaded
+        self.test_partner = self.env["res.partner"].create({"name": "Test Partner"})
 
     def test_get_template(self):
         with mock_request(self.env):
@@ -56,7 +60,7 @@ def test_get_render_values(self):
                 },
             )
             # get a main obj
-            partner = self.env.ref("base.res_partner_12")
+            partner = self.test_partner
             form = self.form_controller.get_form("res.partner", model_id=partner.id)
             self.assertEqual(
                 self.form_controller.get_render_values(form),
@@ -129,7 +133,7 @@ def test_redirect_after_success(self):
             method="POST",
         )
         with mock_request(self.env, httprequest=req.httprequest):
-            partner = self.env.ref("base.res_partner_12")
+            partner = self.test_partner
             response = self.form_controller.make_response(
                 "res.partner", model_id=partner.id
             )
@@ -143,6 +147,25 @@ def test_redirect_after_success(self):
 
 @unittest.skipIf(os.getenv("SKIP_HTTP_CASE"), "HTTP case disabled.")
 class TestControllersRender(FormHttpTestCase):
+    @classmethod
+    def setUpClass(cls):
+        super().setUpClass()
+        # Warm up frontend QWeb rendering (`web.frontend_layout` /
+        # `portal.portal_layout`, which pulls in `portal.language_selector`)
+        # once here, before any real HTTP request is made.
+        # Compiling/preparing the frontend qweb env for the very first time
+        # races with `ir.qweb._prepare_frontend_environment`: `languages` can
+        # end up unset, causing a sporadic 500 on the first HTTP request
+        # (confirmed on real OCA CI, not just locally).
+        # We use `website`'s bare `MockRequest` here rather than our own
+        # `mock_request` helper: the latter deliberately empties
+        # `registry._init_modules` for its own purposes, which breaks asset
+        # bundle lookups needed to actually render this template.
+        with MockRequest(cls.env):
+            cls.env["ir.qweb"].with_context(lang="en_US")._render(
+                "portal.portal_layout", {}
+            )
+
     def setUp(self):
         super().setUp()
         self.authenticate("admin", "admin")
@@ -193,7 +216,8 @@ def test_default_create_rendering(self):
         self._check_rendering(dom, "cms.form.res.partner", "res.partner", "create")
 
     def test_default_edit_rendering(self):
-        partner = self.env.ref("base.res_partner_1")
+        # do not rely on demo data (eg: `base.res_partner_1`) being loaded
+        partner = self.env["res.partner"].create({"name": "Test Partner"})
         dom = self.html_get("/cms/edit/res.partner/{}".format(partner.id))
         self._check_rendering(dom, "cms.form.res.partner", "res.partner", "edit")
 
diff --git a/cms_form/tests/test_form_base.py b/cms_form/tests/test_form_base.py
index de320761..93303580 100644
--- a/cms_form/tests/test_form_base.py
+++ b/cms_form/tests/test_form_base.py
@@ -6,6 +6,7 @@
 from werkzeug.wrappers import Request
 
 from odoo import http
+from odoo.tests.common import new_test_user
 
 from .common import FormTestCase
 from .utils import fake_request
@@ -183,7 +184,8 @@ def test_fields_binary(self):
 
     def test_fields_protected(self):
         group = self.env.ref("base.group_system")
-        user = self.env.ref("base.user_demo")
+        # plain internal user, not relying on demo data being loaded
+        user = new_test_user(self.env, login="test_fields_protected_user")
         # user does not have the group
         self.assertNotIn(group, user.groups_id)
         form = self.get_form("cms.form.protected.fields", sudo_uid=user.id)
diff --git a/cms_form/tests/test_form_render.py b/cms_form/tests/test_form_render.py
index 45705b8e..f0a4c969 100644
--- a/cms_form/tests/test_form_render.py
+++ b/cms_form/tests/test_form_render.py
@@ -1,6 +1,8 @@
 # Copyright 2017 Simone Orsi
 # License LGPL-3.0 or later (http://www.gnu.org/licenses/lgpl.html).
 
+from odoo.tests.common import new_test_user
+
 from .common import FormRenderTestCase
 
 
@@ -100,7 +102,8 @@ def test_render_form_fieldsets_get(self):
 
     def test_render_form_fieldsets_protected_field(self):
         """No field, no fieldset."""
-        user = self.env.ref("base.user_demo")
+        # plain internal user, not relying on demo data being loaded
+        user = new_test_user(self.env, login="test_render_fieldsets_protected_user")
         form = self.get_form("cms.form.test_fieldsets", sudo_uid=user.id)
         html = form.form_render()
         node = self.to_xml_node(html)[0]
diff --git a/cms_form/tests/utils.py b/cms_form/tests/utils.py
index cccd6479..d3b8ecd9 100644
--- a/cms_form/tests/utils.py
+++ b/cms_form/tests/utils.py
@@ -77,9 +77,17 @@ def mock_request(
         for k, v in httprequest_attrs.items():
             setattr(mocked_request.httprequest, k, v)
         mocked_request.make_response = lambda data, **kw: data
+        # `MockRequest` exposes the real (shared, process-wide) registry, not a copy.
+        # Mutating `_init_modules` here used to leak into every other test running
+        # afterwards (breaking asset bundling and HTTP routing map generation for
+        # the rest of the test run), so make sure to restore it once done.
+        original_init_modules = mocked_request.registry._init_modules
         mocked_request.registry._init_modules = set()
         mocked_request.session.touch = lambda: True
-        yield mocked_request
+        try:
+            yield mocked_request
+        finally:
+            mocked_request.registry._init_modules = original_init_modules
 
 
 class FakeSessionStore(SessionStore):
diff --git a/cms_form/tests/widgets/test_widget_x2many.py b/cms_form/tests/widgets/test_widget_x2many.py
index 3c1ab691..6ef13bf7 100644
--- a/cms_form/tests/widgets/test_widget_x2many.py
+++ b/cms_form/tests/widgets/test_widget_x2many.py
@@ -80,7 +80,11 @@ def test_widget_x2many_base_load(self):
         )
 
     def test_widget_x2many_base_load_from_record(self):
-        categs = self.env["res.partner.category"].search([], limit=3)
+        # Do not rely on demo data or other modules' data being present:
+        # create dedicated categories so the test is self-contained.
+        categs = self.env["res.partner.category"].create(
+            [{"name": f"Fake category {i}"} for i in range(3)]
+        )
         partner = self.partners[0]
         form = fake_form(
             self.env,