How to check expected log in the middle of a running function using Jest unit testing?

I have this demo function:

export async function myHandler(
    param1: string,
    param2: string,
    req: Request,
    next: NextFunction,

) {
    const log = req.log.prefix(`[my=prefix]`);
    let res;
    If (param1 === 'param1') {
        log("GOT PARAM 1");
    } else {
        res = await doSomething();
    }
    log("GOT HERE");
    ..
    ..
    ..
    ..
    res.setReturnStatus(200)
    }
    next();
}

regarding the logger, this is the request that contains it:

 const req: {
url: string;
params: {};
body: {
    device: {
        type: string;
        p1: string;
        p2: string;
        p3: string;
    };
    data: {
        sample: number;
    };
};
metric: () => jest.Mock<any, any>;
log: {
    (): jest.Mock<any, any>;
    warn(): jest.Mock<...>;
    error(): jest.Mock<...>;
    prefix(): jest.Mock<...>;
};
timing: () => jest.Mock<...>;

}

When I wrote my unit test my line is checking the return status: expect(res.status).toBeCalledWith(200);

I want to cover the first 'if' statement, which logs 'GOT PARAM 1' but can't figure out how to intercept my call in the middle.

doSomething = jest.fn(() => Promise.resolve());
await myHandler('param1', 'param1', next); //HERE to check somehow that also was log ?
expect(res.status).toBeCalledWith(200);

tried to do something like :

const spy = jest.spyOn(req.log, 'log');

got the error:

Cannot spy the log property because it is not a function; undefined given instead