using BDD to test my RxSwift enabled service, how to stop a variable emitting a value when first bound

gistfile1.txt

            context("get messages") {
                var messagesReceived: [Message]?
                var parameterVariable = Variable<GetMessageParams>?((nil,nil,nil,nil))

                beforeEach {
                    MessagesService.observableService(parametersObservable: parameterVariable.asObservable())
                    { (service: MessagesService, params: GetMessageParams, callback: @escaping ([Message]?)->Void) in
                        service.getMessages(params: params) { messages in
                            callback(messages)
                        }
                        }.subscribe(onNext:{ messages in
                            messagesReceived = messages
                        }).addDisposableTo(disposeBag)
                    
                    if let test = test, let wang = wang, let walk = walk {
                        test.addMock(with: "/profile/\(wang.Id)/invite/\(walk.Id)/search-profiles", method: .post, reply: .success(statusCode: 200, body: try! loadSampleJson(jsonFilename: "searchResults")))
                    }
                }
                
                
                it("should get a list of messages on all message boxes") {
                    typealias GetMessageParams = MessagesService.GetMessageParams
                    guard let disposeBag = disposeBag else {
                        expect(false).to(beTrue(), description: "preconditions failed")
                        return
                    }
                    
                    waitUntil { done in
                        parameterVariable.value = (nil,nil,nil,nil)
                        done
                    }