I have a function as such:

export type SendMessageParams = {
  chatSession?: ChatSession,
  // ... other params ...
};

const sendMessage = async ({
  chatSession,
  // ... other params ...
}: SendMessageParams): Promise<void> => {
  // await chatSession?.sendMessage()
  // somewhere in implementation
};

export default sendMessage;

ChatSession is from @google/generative-ai.

I’d like to mock it in my test file as such:

let defaultParams: SendMessageParams;

beforeEach(() => {
  jest.mock('@google/generative-ai', () => ({
    ChatSession: {
      sendMessage: async (content: string) => content,
    },
  }));
  defaultParams = {
    chatSession: new ChatSession('', ''),
    // ... other params ...
  };
});

afterEach(() => {
  jest.clearAllMocks();
});

it('should send message', async () => {
  // await sendMessage();
});

When I run npm run test, I get the error saying:

 FAIL  tests/logic/actions/sendMessage.test.ts
  ● should send message

    ReferenceError: fetch is not defined

      43 |   const sendMessageInner = async (messages: Message[]) => {
      44 |     setMessageListState(messages);
    > 45 |     const result = await chatSession?.sendMessage(content);
         |                    ^
      46 |     const responseText = result?.response.text();
      47 |     if (responseText) {
      48 |       const responseMessage: Message = {

      at makeRequest (node_modules/@google/generative-ai/dist/index.js:246:9)
      at generateContent (node_modules/@google/generative-ai/dist/index.js:655:28)
      at node_modules/@google/generative-ai/dist/index.js:890:25
      at ChatSession.sendMessage (node_modules/@google/generative-ai/dist/index.js:909:9)
      at sendMessageInner (src/logic/actions/sendMessage.ts:45:20)
      at src/logic/actions/sendMessage.ts:72:7
      at sendMessage (src/logic/actions/sendMessage.ts:59:3)
      at Object.<anonymous> (tests/logic/actions/sendMessage.test.ts:44:3)

…which hints that chatSession.sendMessage method still uses the real implementation instead of mock.

I’d like to know why this happens and what the solution would be.

Thanks in advance.

Environment

• Node 20.11.0 (lts/iron)
• Jest 29.7.0
• @google/generative-ai 0.5.0 (if relevant)