How do I invoke a validation attribute for testing?

I ended up using the static Validator class from the DataAnnotations namespace. My test now looks like this:

[TestMethod]
public void PhoneNumberIsValid()
{
    var dude = new Person();
    dude.PhoneNumber = "666-978-6410";

    var result = Validator.TryValidateObject(dude, new ValidationContext(dude, null, null), null, true);

    Assert.IsTrue(result);
}

Just new up a RegularExpressionAttribute object.

var regularExpressionAttribute = new RegularExpressionAttribute("pattern");

Assert.IsTrue(regularExpressionAttribute.IsValid(objToTest));

Sorry for answering late.

I'm new here. If you want test every ValidationAttribute in isolate you can proceed to the next manner for example:

    [Test]
    public void Test_the_State_value_IsRequired()
    {
        string value = "Finished";
        var propertyInfo = typeof(TimeoffTemporalIncapacityEntry).GetProperty("State");
        var attribute = propertyInfo.GetCustomAttributes(typeof(RequiredAttribute), true).Cast<RequiredAttribute>().FirstOrDefault();
        Assert.IsTrue(attribute.IsValid(value));
    }