How can i write unit test for this actionfilter - unit-testing

Question

public MyContext _db;
public override void OnActionExecuted(HttpActionExecutedContext actionExecutedContext)
{
if (_db == null || !_db.ChangeTracker.HasChanges())
{
return;
}
try
{
_db.SaveChanges();
}
catch
{
}
}
This is my action filter for my wep api project. _db context object injected to this filter by per request. My point is here to call SaveChanges() method once after all processing done in service layers. My problem is how can test this filter? How can i mimic exception case that can happen in any controler or service layer and when exception throws saveChanges() never called? How can i setup the case that exception occurred in any place inside application?

Answer 1

I have been doing the same, last week, for my WebAPI 2 action filter.
I have an action filter that validates my ModelState and in case of any error it throws an error list with 200 HTTPcode.
The action looks like this:
public class ModelValidationActionFilterAttribute : ActionFilterAttribute
{
public override void OnActionExecuting(HttpActionContext actionContext)
{
var modelState = actionContext.ModelState;
if (!modelState.IsValid)
{
actionContext.Response = ...
}
}
}
UNIT TEST
var httpControllerContext = new HttpControllerContext
{
Request = new HttpRequestMessage(HttpMethod.Post, "http://localhost/someUri")
{
Content = new ObjectContent(typeof(MyModel),
new MyModel(), new JsonMediaTypeFormatter())
},
RequestContext = new HttpRequestContext()
};
httpControllerContext.Request = new HttpRequestMessage();
httpControllerContext.Request.SetConfiguration(new HttpConfiguration());
var httpActionContext = new HttpActionContext { ControllerContext = httpControllerContext };
var filter = new ModelValidationActionFilterAttribute();
httpActionContext.ModelState.AddModelError("*", "Invalid model state");
// act
filter.OnActionExecuting(httpActionContext);
// assert
httpActionContext.Response.ShouldNotBe(null);
httpActionContext.Response.ShouldBeOfType(typeof (HttpResponseMessage));
var result = httpActionContext.Response.Content.ReadAsStringAsync().Result;
BaseServiceResponse<object> resultResponse =
JsonConvert.DeserializeObject<BaseServiceResponse<object>>(result);
resultResponse.Data.ShouldBe(null);
resultResponse.Messages.Count.ShouldBe(1);
resultResponse.Messages.First().Description.ShouldBe("Invalid model state");
In your case you need to Mock DB context using IDbContext interface - see here: http://aikmeng.com/post/62817541825/how-to-mock-dbcontext-and-dbset-with-moq-for-unit

Answer 2

If an unhandled exception occurs while executing the request then the Exception property on actionExecutedContext will contain the exception. This is part of the framework, and not something you need to test. In your tests you can simple set the Exception property manually and assert that the attribute takes the correct action.
[Fact]
public void Saves_data_on_failure()
{
var mockDbContext = new Mock<IDbContext>();
var myAttribute = new MyAttribute(mockDbContext.Object);
var executionContext = new HttpActionExecutedContext
{
Exception = new Exception("Request failed.")
};
myAttribute.OnActionExecuted(executionContext);
mockDbContext.Verify(d => d.SaveChanges());
}
You might also want to consider whether or not you want to save data for all types of exception. The data might be in an invalid/unknown state.