litellm_fix_mapped_tests_core: fix test isolation and mock injection issues

## Problem
Four tests in litellm_mapped_tests_core were failing:
1. test_register_model_with_scientific_notation - KeyError due to test isolation issues
2. test_search_uses_registry_credentials - Mock not being called due to incorrect patch path
3. test_send_email_missing_api_key - Real API calls despite mocking
4. test_stream_transformation_error_sync - Mock not effective, real API called

## Solution

### test_register_model_with_scientific_notation
- Use unique model name to avoid conflicts with other tests
- Clear LRU caches before test to prevent stale data
- Clean up model_cost entry after test

### test_search_uses_registry_credentials
- Use patch.object() on the actual base_llm_http_handler instance
- String-based patching for instance methods can fail; direct object patching is more reliable

### test_send_email_missing_api_key
- Directly inject mock HTTP client into logger instance
- This bypasses any caching issues that could cause the fixture mock to be ineffective

### test_stream_transformation_error_sync
- Patch litellm.completion directly instead of the handler module's litellm reference
- This ensures the mock is effective regardless of import order

## Regression
These tests were affected by LRU caching added in #19606 and HTTP client caching.

tests/test_litellm/enterprise/enterprise_callbacks/send_emails/test_resend_email.py

@@ -98,7 +98,7 @@ async def test_send_email_success(mock_env_vars, mock_httpx_client):
 
 @pytest.mark.asyncio
 @respx.mock
-async def test_send_email_missing_api_key(mock_httpx_client):
+async def test_send_email_missing_api_key():
     # Block all HTTP requests at network level to prevent real API calls
     respx.post("https://api.resend.com/emails").mock(
         return_value=httpx.Response(200, json={"id": "test_email_id"})
@@ -117,13 +117,18 @@ async def test_send_email_missing_api_key(mock_httpx_client):
         subject = "Test Subject"
         html_body = "<p>Test email body</p>"
 
-        # Mock the response to avoid making real HTTP requests
+        # Create mock HTTP client and inject it directly into the logger
+        # This ensures the mock is used regardless of any caching issues
         mock_response = mock.Mock(spec=Response)
         mock_response.raise_for_status.return_value = None
-
         mock_response.status_code = 200
         mock_response.json.return_value = {"id": "test_email_id"}
-        mock_httpx_client.post.return_value = mock_response
+        
+        mock_async_client = mock.AsyncMock()
+        mock_async_client.post.return_value = mock_response
+        
+        # Directly inject the mock client to bypass any caching
+        logger.async_httpx_client = mock_async_client
 
         # Send email
         await logger.send_email(
@@ -131,8 +136,8 @@ async def test_send_email_missing_api_key(mock_httpx_client):
         )
 
         # Verify the HTTP client was called with None as the API key
-        mock_httpx_client.post.assert_called_once()
-        call_args = mock_httpx_client.post.call_args
+        mock_async_client.post.assert_called_once()
+        call_args = mock_async_client.post.call_args
         assert call_args[1]["headers"] == {"Authorization": "Bearer None"}
     finally:
         # Restore the original key if it existed

tests/test_litellm/google_genai/test_google_genai_handler.py

@@ -183,10 +183,8 @@ def test_stream_transformation_error_sync():
         "translate_completion_output_params_streaming", 
         return_value=None
     ):
-        # Mock litellm.completion at the module level where it's imported
-        # We need to patch it in the handler module, not in litellm itself
-        with patch("litellm.google_genai.adapters.handler.litellm") as mock_litellm:
-            mock_litellm.completion.return_value = mock_stream
+        # Patch litellm.completion directly to prevent real API calls
+        with patch("litellm.completion", return_value=mock_stream):
             # Call the handler with stream=True and expect a ValueError
             with pytest.raises(ValueError, match="Failed to transform streaming response"):
                 GenerateContentToCompletionHandler.generate_content_handler(

tests/test_litellm/test_utils.py

@@ -2282,8 +2282,19 @@ def test_register_model_with_scientific_notation():
     """
     Test that the register_model function can handle scientific notation in the model name.
     """
+    # Use a unique model name to avoid conflicts with other tests
+    test_model_name = "test-scientific-notation-model-unique-12345"
+    
+    # Clean up any pre-existing entry and clear caches
+    if test_model_name in litellm.model_cost:
+        del litellm.model_cost[test_model_name]
+    
+    # Clear LRU caches that might have stale data
+    from litellm.utils import get_model_info, _cached_get_model_info_helper, _invalidate_model_cost_lowercase_map
+    _invalidate_model_cost_lowercase_map()
+    
     model_cost_dict = {
-        "my-custom-model": {
+        test_model_name: {
             "max_tokens": 8192,
             "input_cost_per_token": "3e-07",
             "output_cost_per_token": "6e-07",
@@ -2294,12 +2305,17 @@ def test_register_model_with_scientific_notation():
 
     litellm.register_model(model_cost_dict)
 
-    registered_model = litellm.model_cost["my-custom-model"]
+    registered_model = litellm.model_cost[test_model_name]
     print(registered_model)
     assert registered_model["input_cost_per_token"] == 3e-07
     assert registered_model["output_cost_per_token"] == 6e-07
     assert registered_model["litellm_provider"] == "openai"
     assert registered_model["mode"] == "chat"
+    
+    # Clean up after test
+    if test_model_name in litellm.model_cost:
+        del litellm.model_cost[test_model_name]
+    _invalidate_model_cost_lowercase_map()
 
 
 def test_reasoning_content_preserved_in_text_completion_wrapper():

tests/test_litellm/vector_stores/test_vector_store_registry.py

@@ -136,6 +136,9 @@ def test_add_vector_store_to_registry():
 @respx.mock
 def test_search_uses_registry_credentials():
     """search() should pull credentials from vector_store_registry when available"""
+    # Import the actual instance to patch it correctly
+    from litellm.vector_stores.main import base_llm_http_handler
+    
     # Block all HTTP requests at the network level to prevent real API calls
     respx.route().mock(return_value=httpx.Response(200, json={"object": "list", "data": []}))
     
@@ -168,8 +171,9 @@ def test_search_uses_registry_credentials():
         ) as mock_get_creds, patch(
             "litellm.vector_stores.main.ProviderConfigManager.get_provider_vector_stores_config",
             return_value=MagicMock(),
-        ), patch(
-            "litellm.vector_stores.main.base_llm_http_handler.vector_store_search_handler",
+        ), patch.object(
+            base_llm_http_handler,
+            "vector_store_search_handler",
             return_value=mock_search_response,
         ) as mock_handler:
             search(vector_store_id="vs1", query="test", litellm_logging_obj=logger)