function expectSingleEchoDeliveryCall() {

expect(mockDeliverOutboundPayloads).toHaveBeenCalledOnce();

const firstCall = mockDeliverOutboundPayloads.mock.calls[0];

const firstCall = mockDeliverOutboundPayloads.mock.calls.at(0);

if (!firstCall) {

throw new Error("Expected echo transcript delivery call");

}