add test for custom_domain

tests/dashboard/test_custom_domain.py

@@ -0,0 +1,19 @@
+from flask import url_for
+
+from app.extensions import db
+from tests.utils import login
+
+
+def test_add_domain_success(flask_client):
+    user = login(flask_client)
+    user.lifetime = True
+    db.session.commit()
+
+    r = flask_client.post(
+        url_for("dashboard.custom_domain"),
+        data={"form-name": "create", "domain": "ab.cd"},
+        follow_redirects=True,
+    )
+
+    assert r.status_code == 200
+    assert b"New domain ab.cd is created" in r.data