test(router): test litellm.Router fallbacks initialization and list parsing

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
+    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 == []