UTA_MultipleExpectedExceptionsOnTestMethod is unused

[Youssef1313]

IMO, instead of using it and issue a warning at runtime, this could be switched to an analyzer.

[Youssef1313]

@Evangelink Thoughts? I'm also not sure "when" did the resource became unused.

Note that while the attribute's AllowMultiple is false (default), we may still need to issue some sort of warning here for the niche scenario of the user defining his own attribute. The following will compile today even though AllowMultiple is false.

    public class MyExpectedExceptionAttribute : ExpectedExceptionBaseAttribute
    {
        protected override void Verify(Exception exception) => throw new NotImplementedException();
    }

    [TestMethod]
    [ExpectedException(typeof(Exception))]
    [MyExpectedException]
    public void Test() { }

Or even:

[AttributeUsage(AttributeTargets.Method, AllowMultiple = true)]
public class MyExpectedExceptionAttribute : ExpectedExceptionBaseAttribute
{
    protected override void Verify(Exception exception) => throw new NotImplementedException();
}

[TestMethod]
[MyExpectedException]
[MyExpectedException]
public void Test() { }

[Youssef1313]

The behavior of issuing a warning on multiple attributes regressed on #2839 which is quite recent.