Testing NServiceBus Behavior with custom Handler

Question

I have a MessageHandler with a custom attribute on it. The behavior I'm testing does something based on the value of that attribute. The NServicebus documentation only gives unit tests examples of a behavior based on a mocked handler. How can I use my own fake or is there an other way I should test my behavior?

// A fake message handler containing the attribute
[ExecuteHandler(true)]
class FakeHandler : IHandleMessages<FakeCommand>
{
  public Task Handle(FakeCommand message, IMessageHandlerContext context) => Task.CompletedTask;
}

[Test]
public async Task Invoke_GivenHandlerWithoutAttribute_InvokeNext()
{
  // Given
  var handlerExecuted = false;
  var context = new TestableMessageHandlerContext
  {
    // I want to add my fake handler to the context so I can test if it gets executed. Problem is that I can't cast my handler to type MessageHandler
    // MessageHandler = new FakeHandler(),
  }

  // When
  await _behavior.Invoke(context, () =>
  {
    handlerExecuted = true;
    return Task.CompletedTask;
  });

  // Then
  handlerExecuted.Should().BeTrue();
}

Thijs · Accepted Answer · 2021-03-16T07:52:22.943

To answer my own question. I made it work by letting my handlers inherit MessageHandler.

[Test]
public async Task Invoke_GivenHandlerWithAttributeTrue_InvokeNext()
{
  // Given
  var handlerExecuted = false;
  var context = new TestableMessageHandlerContext
  {
    MessageHandler = new MessageHandler(null, typeof(FakeHandler)),
  }
  
  // When
  await _behavior.Invoke(context, () =>
  {
    handlerExecuted = true;
    return Task.CompletedTask;
  });

  // Then
  handlerExecuted.Should().BeTrue();
}

[Test]
public async Task Invoke_GivenHandlerWithAttributeFalse_DoesNotInvokeNext()
{
  // Given
  var handlerExecuted = false;
  var context = new TestableMessageHandlerContext
  {
    MessageHandler = new MessageHandler(null, typeof(FakeHandlerNotExecuting)),
  }
  
  // When
  await _behavior.Invoke(context, () =>
  {
    handlerExecuted = true;
    return Task.CompletedTask;
  });

  // Then
  handlerExecuted.Should().BeFalse();
}

[ExecuteHandler(true)]
class FakeHandler: IHandleMessages<FakeCommand>
{
  public Task Handle(FakeCommand message, IMessageHandlerContext context) => Task.CompletedTask;
}

[ExecuteHandler(false)]
class FakeHandlerNotExecuting: IHandleMessages<FakeCommand>
{
  public Task Handle(FakeCommand message, IMessageHandlerContext context) => Task.CompletedTask;
}

Testing NServiceBus Behavior with custom Handler

1 Answers1