From cdeeb38be4e6af464685f55d316f1c4be78cf38d Mon Sep 17 00:00:00 2001
From: Nikhil Jangid <161968345+nikhiljangid120@users.noreply.github.com>
Date: Sat, 3 Oct 2026 01:31:21 -0500
Subject: [PATCH] test: cover generation engine defaults

Verify omitted engines remain unset while explicit values are validated.
---
 .../test_generation_engine_resolution.py      | 27 +++++++++++++++++++
 1 file changed, 27 insertions(+)
 create mode 100644 backend/tests/test_generation_engine_resolution.py

diff --git a/backend/tests/test_generation_engine_resolution.py b/backend/tests/test_generation_engine_resolution.py
new file mode 100644
index 00000000..7cd3dc34
--- /dev/null
+++ b/backend/tests/test_generation_engine_resolution.py
@@ -0,0 +1,27 @@
+"""Tests for generation request engine selection."""
+
+import pytest
+from pydantic import ValidationError
+
+from backend import models
+
+
+def _request(**kwargs) -> models.GenerationRequest:
+    return models.GenerationRequest(profile_id="profile-1", text="hello", **kwargs)
+
+
+def test_omitted_engine_does_not_override_profile_default():
+    request = _request()
+
+    assert request.engine is None
+
+
+def test_explicit_engine_is_preserved():
+    request = _request(engine="chatterbox")
+
+    assert request.engine == "chatterbox"
+
+
+def test_invalid_explicit_engine_is_rejected():
+    with pytest.raises(ValidationError):
+        _request(engine="invalid")