How to use xUnit to test code when Azure Service bus throws Transient exceptions

Question

I have an Azure Service Bus Trigger function that has the job of replicating the incoming message from a topic and sending it to another service bus topic.

I send the incoming message to the service bus in the other region using Azure.Messaging.ServiceBus.ServiceBusSender.SendMessageAsync()

I need to write a xUnit test to ensure the right behaviour is being followed when the topic/service bus in the other region is unavailable. Is there a way to simulate the SendMessageAsync() method throwing one of the transient exceptions to test this?

Answer 1

You can mock ServiceBusSender.

e.g. using NSubstitute + xUnit

[Fact]
public void Test1()
{
    // Arrange
    var mockSender = Substitute.For<ServiceBusSender>();
    mockSender.SendMessageAsync(default).ThrowsForAnyArgs(new Exception("Example exception"));

    // Act
    var testClass = new YourClass(mock);
    testClass.DoSomething();

    // Assert
}