public async Task ServiceBusTopicMessenger_ReceiveSetupError() { // Arrange var config = new ConfigurationBuilder().AddJsonFile("appSettings.json").Build(); var testMessenger = new ServiceBusMessenger(new ConnectionConfig() { ConnectionString = config.GetValue <string>("ConnectionString"), }); // Act/Assert Assert.Throws <InvalidOperationException>(() => testMessenger.Receive <string>((msg) => { }, (err) => { })); Assert.Null(testMessenger.ReceiveOne <string>()); await Assert.ThrowsAsync <NullReferenceException>(() => testMessenger.Send("test")); }