How to use the google-auth-library.OAuth2Client.prototype function in google-auth-library

beforeEach(() => {
      voxaApp = new VoxaApp({ views, variables });
      googleAction = new GoogleAssistantPlatform(voxaApp, { clientId: "clientId" });

      const userDetailsMocked: any = _.cloneDeep(googleResponse);

      simple
        .mock(OAuth2Client.prototype, "verifySignedJwtWithCerts")
        .returnWith({
          getPayload: () => {
            return userDetailsMocked;
          },
        });
    });