Mocking GraphCypherQAChain in Python unit test cases

chain.py
----------------------------------
from langchain.chains import GraphCypherQAChain
from langchain_openai import ChatOpenAI
from langchain_community.graphs import Neo4jGraph
from langchain.prompts.prompt import PromptTemplate

import os

OPENAI_API_KEY = os.getenv("OPENAI_API_KEY")

graph = Neo4jGraph(
    url=os.getenv("NEO4J_URI"),
    username=os.getenv("NEO4J_USERNAME"),
    password=os.getenv("NEO4J_PASSWORD"),
    sanitize=True,
)

graph_chain = GraphCypherQAChain.from_llm(
    graph=graph,
    cypher_llm=ChatOpenAI(temperature=0, model="gpt-3.5-turbo"),
    qa_llm=ChatOpenAI(temperature=0, model="gpt-3.5-turbo-16k"),
    verbose=True,
    return_intermediate_steps=True,
    validate_cypher=True,
    top_k=100,
)

------------------------------------------------------
main.py
------------------------------------------------------
from chain import graph_chain

def generate(question: str) -> str:
  
    chain_result = graph_chain.invoke(
         {"query": question},
         return_only_outputs=False,
    )
    return chain_result['result']

I am trying to write unit test case for main.py.

test_main.py
----------------------------------------------
from main import generate

question = "mock_question"

class mock_GraphCypherQAChain:
    def invoke(cls, a=None, return_only_outputs=False):
        return {
            "result": "Some completion",
            "intermediate_steps": [{"query": question}],
        }

@mock.patch('main.graph_chain')
def test_generate_for_valid_chain_result(mock_graph_chain):
    mock_graph_chain.return_value = mock_GraphCypherQAChain()
    actual_output = "Some completion"
    
    test_output = generate(question)

    assert actual_output == test_output

But I am getting the test case failed as -

FAILED tests/test_main.py::test_generate_for_valid_chain_result - ValueError: Could not find result in chain_result

The mock mock_graph_chain.invoke() is returning a MagicMock object as below, instead of the dict given -

<MagicMock name='graph_chain.invoke()' id='139624876920784'>

How can I resolve this?