function customFlowSwitchTest(flow, shouldReceive, sendPayload, done) {
        customFlowMessageSwitchTest(flow,shouldReceive,{payload: sendPayload}, done);
    }
Execute a switch test. Can specify whether the should node is expected to send a payload onwards to the helper node.
The flow and the payload can be customised
@param flow - the custom flow to be tested => must contain a switch node (switchNode1) wiring a helper node (helperNode1)
@param shouldReceive - whether the helper node should receive a payload
@param sendPayload - the payload message we're sending
@param done - callback when done