fix(caching.py): dual cache async_batch_get_cache fix + testing

this fixes a bug in usage-based-routing-v2 which was caused b/c of how the result was being returned from dual cache async_batch_get_cache. it also adds unit testing for that function (and it's sync equivalent)

litellm/tests/test_caching.py

@@ -33,6 +33,51 @@ def generate_random_word(length=4):
 messages = [{"role": "user", "content": "who is ishaan 5222"}]
 
 
+@pytest.mark.asyncio
+async def test_dual_cache_async_batch_get_cache():
+    """
+    Unit testing for Dual Cache async_batch_get_cache()
+    - 2 item query
+    - in_memory result has a partial hit (1/2)
+    - hit redis for the other -> expect to return None
+    - expect result = [in_memory_result, None]
+    """
+    from litellm.caching import DualCache, InMemoryCache, RedisCache
+
+    in_memory_cache = InMemoryCache()
+    redis_cache = RedisCache()  # get credentials from environment
+    dual_cache = DualCache(in_memory_cache=in_memory_cache, redis_cache=redis_cache)
+
+    in_memory_cache.set_cache(key="test_value", value="hello world")
+
+    result = await dual_cache.async_batch_get_cache(keys=["test_value", "test_value_2"])
+
+    assert result[0] == "hello world"
+    assert result[1] == None
+
+
+def test_dual_cache_batch_get_cache():
+    """
+    Unit testing for Dual Cache batch_get_cache()
+    - 2 item query
+    - in_memory result has a partial hit (1/2)
+    - hit redis for the other -> expect to return None
+    - expect result = [in_memory_result, None]
+    """
+    from litellm.caching import DualCache, InMemoryCache, RedisCache
+
+    in_memory_cache = InMemoryCache()
+    redis_cache = RedisCache()  # get credentials from environment
+    dual_cache = DualCache(in_memory_cache=in_memory_cache, redis_cache=redis_cache)
+
+    in_memory_cache.set_cache(key="test_value", value="hello world")
+
+    result = dual_cache.batch_get_cache(keys=["test_value", "test_value_2"])
+
+    assert result[0] == "hello world"
+    assert result[1] == None
+
+
 # @pytest.mark.skip(reason="")
 def test_caching_dynamic_args():  # test in memory cache
     try: