From 710e08079b60976ff605f08b8e8f682d8513b99f Mon Sep 17 00:00:00 2001
From: Kartik Chilkoti <chilkotikartik@gmail.com>
Date: Wed, 16 Sep 2026 17:01:47 +0530
Subject: [PATCH 1/2] test(router): add fallback chain traversal and priority
 tier routing tests [skip ci]

---
 tests/test_router_fallback_chain.py | 36 +++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)
 create mode 100644 tests/test_router_fallback_chain.py

diff --git a/tests/test_router_fallback_chain.py b/tests/test_router_fallback_chain.py
new file mode 100644
index 00000000000..38e60334c39
--- /dev/null
+++ b/tests/test_router_fallback_chain.py
@@ -0,0 +1,36 @@
+\"\"\"
+Unit tests for model fallback chain resolution and priority sequence bounds in LiteLLM router.
+\"\"\"
+import pytest
+from typing import List, Dict, Any
+
+def test_fallback_chain_traversal():
+    fallback_map = {
+        "gpt-4o": ["azure/gpt-4o-east", "bedrock/claude-3-5-sonnet", "vertex_ai/gemini-1.5-pro"]
+    }
+    
+    primary_model = "gpt-4o"
+    fallbacks = fallback_map.get(primary_model, [])
+    
+    assert len(fallbacks) == 3
+    assert fallbacks[0] == "azure/gpt-4o-east"
+    assert fallbacks[1] == "bedrock/claude-3-5-sonnet"
+    assert fallbacks[2] == "vertex_ai/gemini-1.5-pro"
+
+def test_empty_fallback_graceful_handling():
+    fallback_map: Dict[str, List[str]] = {}
+    requested_model = "unknown-custom-model"
+    fallbacks = fallback_map.get(requested_model, [])
+    assert fallbacks == []
+    assert len(fallbacks) == 0
+
+def test_priority_tier_routing_selection():
+    deployments = [
+        {"model_name": "gpt-4", "tier": "primary", "weight": 80},
+        {"model_name": "gpt-4", "tier": "secondary", "weight": 20}
+    ]
+    
+    total_weight = sum(d["weight"] for d in deployments)
+    assert total_weight == 100
+    primary = [d for d in deployments if d["tier"] == "primary"][0]
+    assert primary["weight"] == 80
\ No newline at end of file

From 103e14e23a2ffe86ee9b1e3f661dff43dac02e49 Mon Sep 17 00:00:00 2001
From: Kartik Chilkoti <chilkotikartik@gmail.com>
Date: Wed, 16 Sep 2026 20:18:16 +0530
Subject: [PATCH 2/2] test(router): test litellm.Router fallbacks
 initialization and list parsing

---
 tests/test_router_fallback_chain.py | 56 ++++++++++++-----------------
 1 file changed, 23 insertions(+), 33 deletions(-)

diff --git a/tests/test_router_fallback_chain.py b/tests/test_router_fallback_chain.py
index 38e60334c39..79b94260382 100644
--- a/tests/test_router_fallback_chain.py
+++ b/tests/test_router_fallback_chain.py
@@ -1,36 +1,26 @@
-\"\"\"
-Unit tests for model fallback chain resolution and priority sequence bounds in LiteLLM router.
-\"\"\"
 import pytest
-from typing import List, Dict, Any
+from litellm import Router
 
-def test_fallback_chain_traversal():
-    fallback_map = {
-        "gpt-4o": ["azure/gpt-4o-east", "bedrock/claude-3-5-sonnet", "vertex_ai/gemini-1.5-pro"]
-    }
-    
-    primary_model = "gpt-4o"
-    fallbacks = fallback_map.get(primary_model, [])
-    
-    assert len(fallbacks) == 3
-    assert fallbacks[0] == "azure/gpt-4o-east"
-    assert fallbacks[1] == "bedrock/claude-3-5-sonnet"
-    assert fallbacks[2] == "vertex_ai/gemini-1.5-pro"
-
-def test_empty_fallback_graceful_handling():
-    fallback_map: Dict[str, List[str]] = {}
-    requested_model = "unknown-custom-model"
-    fallbacks = fallback_map.get(requested_model, [])
-    assert fallbacks == []
-    assert len(fallbacks) == 0
-
-def test_priority_tier_routing_selection():
-    deployments = [
-        {"model_name": "gpt-4", "tier": "primary", "weight": 80},
-        {"model_name": "gpt-4", "tier": "secondary", "weight": 20}
+def test_router_fallbacks_initialization():
+    fallbacks = [
+        {"gpt-4": ["azure/gpt-4-east", "bedrock/claude-3-5-sonnet"]}
     ]
-    
-    total_weight = sum(d["weight"] for d in deployments)
-    assert total_weight == 100
-    primary = [d for d in deployments if d["tier"] == "primary"][0]
-    assert primary["weight"] == 80
\ No newline at end of file
+    router = Router(
+        model_list=[
+            {"model_name": "gpt-4", "litellm_params": {"model": "azure/gpt-4-east"}},
+            {"model_name": "azure/gpt-4-east", "litellm_params": {"model": "azure/gpt-4-east"}},
+            {"model_name": "bedrock/claude-3-5-sonnet", "litellm_params": {"model": "bedrock/claude-3-5-sonnet"}},
+        ],
+        fallbacks=fallbacks,
+    )
+    assert router.fallbacks == fallbacks
+    assert len(router.fallbacks) == 1
+    assert "gpt-4" in router.fallbacks[0]
+
+def test_router_empty_fallbacks():
+    router = Router(
+        model_list=[
+            {"model_name": "gpt-3.5-turbo", "litellm_params": {"model": "gpt-3.5-turbo"}}
+        ]
+    )
+    assert router.fallbacks is None or router.fallbacks == []
\ No newline at end of file