@@ -0,0 +1,76 @@
+import pytest
+import asyncio
+import re
+from src.api.routes.generation import content_generator
+
+@pytest.mark.anyio
+async def test_concurrent_followup_generations(async_client, mock_litellm_completion):
+    # Dynamic mock side_effect to generate output corresponding to the client name
+    async def mock_acompletion(messages, **kwargs):
+        # Extract client name from user message content
+        user_msg = messages[-1]["content"]
+        match = re.search(r"- Client: ([^\n]+)", user_msg)
+        client_name = match.group(1).strip() if match else "Unknown"
+        
+        content = f"Subject: Overdue Notice: {client_name}\nBody:\nHello {client_name}, this is your custom invoice reminder."
+        return mock_litellm_completion.create_response(content=content)
+        
+    mock_litellm_completion.side_effect = mock_acompletion
+    
+    headers = {"X-Service-Key": "test-service-key"}
+    
+    async def fire_request(i):
+        payload = {
+            "invoice_id": f"inv_{i}",
+            "invoice_no": f"INV-{i}",
+            "client_name": f"Client_{i}",
+            "contact_email": f"billing{i}@client.com",
+            "invoice_amount": "100.00",
+            "currency": "USD",
+            "due_date": "2026-07-20",
+            "days_overdue": 5,
+            "urgency_tier": "stage_1_warm",
+            "channel": "email"
+        }
+        response = await async_client.post("/followup", json=payload, headers=headers)
+        assert response.status_code == 200
+        data = response.json()
+        # Assert that the output returned corresponds to the correct client name, ensuring isolation
+        assert data["invoice_id"] == f"inv_{i}"
+        assert data["content"]["subject"] == f"Overdue Notice: Client_{i}"
+        assert f"Hello Client_{i}" in data["content"]["plain_body"]
+        
+    # Fire 10 requests concurrently
+    tasks = [fire_request(i) for i in range(10)]
+    await asyncio.gather(*tasks)
+
+@pytest.mark.anyio
+async def test_concurrent_risk_scoring(async_client):
+    headers = {"X-Service-Key": "test-service-key"}
+    
+    async def fire_risk_request(i):
+        # We vary the amount so the score calculated differs
+        # rule-based: overdue (5/60*0.4=0.033) + amount (i*1000/100000*0.2=0.002*i) + followup (0)
+        # expected score = 0.033 + 0.002 * i
+        payload = {
+            "invoice_id": f"inv_{i}",
+            "features": {
+                "days_overdue": 5,
+                "invoice_amount": float(i * 1000),
+                "followup_count": 0
+            }
+        }
+        # Force rule-based to guarantee deterministic values
+        from src.api.routes.risk import scorer
+        scorer._use_ml_model = False
+        
+        response = await async_client.post("/risk/score", json=payload, headers=headers)
+        assert response.status_code == 200
+        data = response.json()
+        assert data["invoice_id"] == f"inv_{i}"
+        
+        expected_score = round( (5/60.0)*0.4 + (i*1000.0/100000.0)*0.2, 3)
+        assert data["risk_score"] == expected_score
+        
+    tasks = [fire_risk_request(i) for i in range(10)]
+    await asyncio.gather(*tasks)