How to write Unit test for Action that throw HttpException with StatusCode 404 - asp.net-mvc-4

Question

I have a below action in a controller which throw HttpException with status code 404:
public async Task<ActionResult> Edit(int id)
{
Project proj = await _service.GetProjectById(id);
if( proj == null)
{
throw new HttpException(404, "Project not found.");
}
}
To test this scenario, I have written below test case where I am catching AggregationException and rethrowing InnerException which is expected as HttpException:
[TestMethod]
[ExpectedException(typeof(HttpException),"Project not found.")]
public void Edit_Project_Load_InCorrect_Value()
{
Task<ActionResult> task = _projectController.Edit(3);
try
{
ViewResult result = task.Result as ViewResult;
Assert.AreEqual("NotFound", result.ViewName, "Incorrect Page title");
}
catch (AggregateException ex)
{
throw ex.InnerException;
}
}
This test run succefully and return ExpectedException. I have two questions here:
Is this right approach for writing unit test or there is more
gracious way of testing it.
Is this possible to check in Unit Test
that user is getting correct error page( NotFound in this case).

Answer 1

There is a nicer way to test this. We wrote a class called AssertHelpers.cs that has this method in it. The reason this is nicer than ExpectedException is that ExpectedException does not actually verify it was thrown, it just allows the test to pass when it is thrown.
For example, if you change your 404 code to return 200 your test will not fail.
public static void RaisesException<TException>(Action dataFunction, string exceptionIdentifier = null)
{
bool threwException = false;
try
{
dataFunction();
}
catch (Exception e)
{
threwException = true;
Assert.IsInstanceOfType(e, typeof(TException));
if (exceptionIdentifier != null)
Assert.AreEqual(exceptionIdentifier, e.Message);
}
if (!threwException)
Assert.Fail("Expected action to raise exception with message: " + exceptionIdentifier);
}