diff --git a/lemarche/crm/tests.py b/lemarche/crm/tests.py
new file mode 100644
index 000000000..b5e3f7f4a
--- /dev/null
+++ b/lemarche/crm/tests.py
@@ -0,0 +1,92 @@
+from unittest.mock import MagicMock, patch
+
+from django.core.management import call_command
+from django.test import TestCase
+
+from lemarche.siaes.factories import SiaeFactory
+from lemarche.utils.apis.api_brevo import create_or_update_company
+from lemarche.utils.urls import get_object_admin_url, get_object_share_url
+
+
+class CrmBrevoSyncCompaniesCommandTests(TestCase):
+    @classmethod
+    def setUpTestData(cls):
+        """Siae instances initialization"""
+        cls.siae1 = SiaeFactory(name="Test Company 1")
+        cls.siae2 = SiaeFactory()
+
+    @patch("lemarche.utils.apis.api_brevo.sib_api_v3_sdk.Body")
+    def test_create_or_update_company_with_mocked_body(self, mock_body):
+        """Test create_or_update_company with mocked body"""
+        mock_body_instance = MagicMock()
+        mock_body.return_value = mock_body_instance
+
+        create_or_update_company(self.siae1)
+
+        expected_attributes = {
+            "domain": self.siae1.website,
+            "phone_number": self.siae1.contact_phone_display,
+            "app_id": self.siae1.id,
+            "siae": True,
+            "active": self.siae1.is_active,
+            "description": self.siae1.description,
+            "kind": self.siae1.kind,
+            "address_street": self.siae1.address,
+            "address_post_code": self.siae1.post_code,
+            "address_city": self.siae1.city,
+            "contact_email": self.siae1.contact_email,
+            "logo_url": self.siae1.logo_url,
+            "geo_range": self.siae1.geo_range,
+            "app_url": get_object_share_url(self.siae1),
+            "app_admin_url": get_object_admin_url(self.siae1),
+            **self.siae1.extra_data,  # includes completion_rate, tender_email_send_count, etc.
+        }
+
+        mock_body.assert_called_once_with(name="Test Company 1", attributes=expected_attributes)
+
+    @patch("lemarche.utils.apis.api_brevo.create_or_update_company")
+    def test_new_siaes_are_synced_in_brevo(self, mock_create_or_update_company):
+        """Test new siaes are synced in brevo"""
+        call_command("crm_brevo_sync_companies")
+
+        mock_create_or_update_company.assert_any_call(self.siae1)
+        mock_create_or_update_company.assert_any_call(self.siae2)
+        self.assertEqual(mock_create_or_update_company.call_count, 2)
+
+    @patch("lemarche.utils.apis.api_brevo.create_or_update_company")
+    def test_siae_extra_data_is_updated(self, mock_create_or_update_company):
+        """Test siae is updated if extra_data is changed."""
+        initial_extra_data = self.siae2.extra_data.copy()
+
+        self.siae2.completion_rate = 70
+        self.siae2.tender_email_send_count = 10
+        self.siae2.save()
+
+        call_command("crm_brevo_sync_companies", recently_updated=True)
+
+        self.assertTrue(mock_create_or_update_company.called)
+
+        self.siae2.refresh_from_db()
+        expected_extra_data = {
+            "completion_rate": self.siae2.completion_rate,
+            "tender_email_send_count": self.siae2.tender_email_send_count,
+            "recent_tender_detail_click_count": self.siae2.recent_tender_detail_click_count,
+        }
+
+        self.assertNotEqual(initial_extra_data, expected_extra_data, "siae.extra_data aurait dût être mis à jour.")
+
+    @patch("lemarche.utils.apis.api_brevo.create_or_update_company")
+    def test_siae_extra_data_is_not_updated_if_no_change(self, mock_create_or_update_company):
+        """Test siae is not updated if no change in extra_data."""
+        initial_extra_data = self.siae2.extra_data.copy()
+
+        call_command("crm_brevo_sync_companies", recently_updated=True)
+
+        self.assertTrue(mock_create_or_update_company.called)
+
+        self.siae2.refresh_from_db()
+        self.assertEqual(
+            initial_extra_data,
+            self.siae2.extra_data,
+            "siae.extra_data a été mis à jour alors qu'il n'y avait pas de changement.",
+        )