ExpectedException Assert

Question

I need to write a unit test for the next function and I saw I can use [ExpectedException]

this is the function to be tested.

public static T FailIfEnumIs         


        

Answer 1

ExpectedException just asserts that exception of specified type will be thrown by test method:

[TestMethod] 
[ExpectedException(typeof(ArgumentOutOfRangeException))]
public void FailIfEnumIsNotDefined_Check_That_The_Value_Is_Not_Enum()
{
    // PREPARE
    // EXECUTE
    // NO ASSERT!!
}

If you want to assert other parameters of exception, then you should use try..catch in your test method:

[TestMethod]     
public void FailIfEnumIsNotDefined_Check_That_The_Value_Is_Not_Enum()
{
    // PREPARE

    try
    {
       // EXECUTE
       Assert.Fail()
    }
    catch(Exception exception)
    {        
        // ASSERT EXCEPTION DETAILS
    }
}

---

You can write your own method for asserting exception was thrown to avoid repeating same test code over and over again:

public TException AssertCatch(Action action)
    where TException : Exception
{
    try
    {
        action();
    }
    catch (TException exception)
    {
        return exception;
    }

    throw new AssertFailedException("Expected exception of type " + 
                                    typeof(TException) + " was not thrown");
}

Usage:

var exception = AssertCatch(() => /* EXECUTE */);
Assert.AreEqual("foo", exception.Message);