diff --git a/src/config.py b/src/config.py
index 92ae02a..ed5be23 100644
--- a/src/config.py
+++ b/src/config.py
@@ -16,7 +16,7 @@ class Settings(BaseSettings):
     )
 
     # Cohere
-    cohere_api_key: str
+    cohere_api_key: str = ""
     cohere_embed_model: str = "embed-english-v3.0"
     cohere_generate_model: str = "command-nightly"
 
diff --git a/src/services/feedback_engine.py b/src/services/feedback_engine.py
index 6b1c7e1..40fc9f4 100644
--- a/src/services/feedback_engine.py
+++ b/src/services/feedback_engine.py
@@ -1,6 +1,7 @@
 """Intelligent feedback engine for quiz results."""
 
 import logging
+from typing import Any
 
 from src.models.quiz import QuizQuestion
 from src.prompts.feedback import build_feedback_prompt
@@ -34,8 +35,11 @@ def to_dict(self) -> dict:
 class FeedbackEngine:
     """Generates personalized feedback on quiz performance."""
 
-    def __init__(self) -> None:
-        self._client = get_cohere_client()
+    def __init__(self, client: Any = None) -> None:
+        if client is not None:
+            self._client = client
+        else:
+            self._client = get_cohere_client()
 
     def _compute_score(self, user_answers: list[int], correct_answers: list[int]) -> float:
         """Compute score as a percentage."""
diff --git a/tests/test_feedback_engine.py b/tests/test_feedback_engine.py
index 3305232..51e7a10 100644
--- a/tests/test_feedback_engine.py
+++ b/tests/test_feedback_engine.py
@@ -1,5 +1,7 @@
 """Tests for the feedback engine service."""
 
+from unittest.mock import MagicMock
+
 import pytest
 
 from src.models.quiz import QuizQuestion
@@ -11,7 +13,8 @@ class TestFeedbackScoreComputation:
 
     @pytest.fixture
     def engine(self):
-        return FeedbackEngine()
+        mock_client = MagicMock()
+        return FeedbackEngine(client=mock_client)
 
     def test_perfect_score(self, engine):
         user = [0, 1, 2]
@@ -41,7 +44,8 @@ class TestQuickFeedback:
 
     @pytest.fixture
     def engine(self):
-        return FeedbackEngine()
+        mock_client = MagicMock()
+        return FeedbackEngine(client=mock_client)
 
     @pytest.fixture
     def sample_question(self):