I am trying to mock a JavaScript service class (AppInsightsService) that I pass in to a tool class (OrderHistoryTool) to use. I don’t want to return any data from the mock – I just want to ignore all calls to the service functions, and also allow me to pass in the mock when I create my tool that uses that service.

I have tried various and sundry examples that I have seen when searching online, but they are not working for me. I’m sure I’m doing something wrong, but I’m not sure what it is.

Here is a nutshell of the service class that I want to mock:

@Injectable()
export class AppInsightsService {
  constructor(private readonly config: ConfigService) {
...
  }

  async postEvent(appInsightsEventDTO: AppInsightsEventDTO) {
...
  }
...

Here is the tool class that uses the service:

export class OrderHistoryTool extends DynamicStructuredTool {
  constructor(
    ...
    appInsightsService: AppInsightsService,
  ) {
    super({
...
      }),
      func: async (payload: OrderHistoryInput): Promise<string> => {
        appInsightsService.postEvent(
          {
            name: 'OrderHistoryRequested',
            properties: {
              conversationId: conversationId,
              athleteId: athleteId,
            },
          });
...

Here is my test:

const appInsightsServiceMock = jest.mock('../../app-insights/app-insights.service', jest.fn());
import { AppInsightsService } from '../../app-insights/app-insights.service';

enableFetchMocks();

// NOTE: TRIED USING THIS TOO BUT SAME ERROR
// jest.mock('../../app-insights/app-insights.service', () => {
//   return {
//     AppInsightsService: jest.fn().mockImplementation(() => {
//       return jest.fn().mockImplementation(() => {
//         return undefined;
//       });
//     }),
//   };
// });

describe('orderHistory - unit tests', () => {

  it('verify correct output', async () => {

    // NOTE: TRIED USING THIS TOO BUT SAME ERROR
    // const appInsightsServiceMock = jest.fn();

    const orderHistoryTool = new OrderHistoryTool(
      ...
      appInsightsServiceMock as unknown as AppInsightsService,
    );

    const result = await orderHistoryTool.invoke(
      {
        orderNumber: '123456',
      },
    );

I am getting an error when I try to run the test. It is failing when it tries to execute the postEvent() function from the service:

    [tool/error] [1:tool:order_history] [37ms] Tool run errored with error: "appInsightsService.postEvent is not a function
    TypeError: appInsightsService.postEvent is not a functionn    at OrderHistoryTool.func (orderHistory.ts:63:28)n    at OrderHistoryTool._call 

How do I create a mock of the class that will mock all the functions, and allow the user to call those functions as if they are real?