How can I test for an expected exception with a specific exception message from a resource file in Visual Studio Test?

Question

Visual Studio Test can check for expected exceptions using the ExpectedException attribute. You can pass in an exception like this:

[TestMethod] [ExpectedException(typeof(CriticalException))] public void GetOrganisation_MultipleOrganisations_ThrowsException() 

You can also check for the message contained within the ExpectedException like this:

[TestMethod] [ExpectedException(typeof(CriticalException), "An error occured")] public void GetOrganisation_MultipleOrganisations_ThrowsException() 

But when testing I18N applications I would use a resource file to get that error message (any may even decide to test the different localizations of the error message if I want to, but Visual Studio will not let me do this:

[TestMethod] [ExpectedException(typeof(CriticalException), MyRes.MultipleOrganisationsNotAllowed)] public void GetOrganisation_MultipleOrganisations_ThrowsException() 

The compiler will give the following error:

An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute

Does anybody know how to test for an exception that has a message from a resource file?

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One option I have considered is using custom exception classes, but based on often heard advice such as:

"Do create and throw custom exceptions if you have an error condition that can be programmatically handled in a different way than any other existing exception. Otherwise, throw one of the existing exceptions." Source

I'm not expecting to handle the exceptions differently in normal flow (it's a critical exception, so I'm going into panic mode anyway) and I don't think creating an exception for each test case is the right thing to do. Any opinions?

Answer 1

I would recommend using a helper method instead of an attribute. Something like this:

public static class ExceptionAssert {   public static T Throws<T>(Action action) where T : Exception   {     try     {       action();     }     catch (T ex)     {       return ex;     }     Assert.Fail("Exception of type {0} should be thrown.", typeof(T));      //  The compiler doesn't know that Assert.Fail     //  will always throw an exception     return null;   } } 

Then you can write your test something like this:

[TestMethod] public void GetOrganisation_MultipleOrganisations_ThrowsException() {   OrganizationList organizations = new Organizations();   organizations.Add(new Organization());   organizations.Add(new Organization());    var ex = ExceptionAssert.Throws<CriticalException>(               () => organizations.GetOrganization());   Assert.AreEqual(MyRes.MultipleOrganisationsNotAllowed, ex.Message); } 

This also has the benefit that it verifies that the exception is thrown on the line you were expecting it to be thrown instead of anywhere in your test method.

Answer 2

The ExpectedException Message argument does not match against the message of the exception. Rather this is the message that is printed in the test results if the expected exception did not in fact occur.