public void RegularExpressionValidator_NotValidTheory(string s, string pattern)
{
var lessThanOrEqualToValidator = new RegularExpressionValidator <TestValidatableObject>(_ => pattern, ValidationMessageType.Error);
var context = new ValidationContext <TestValidatableObject, string>(null, nameof(TestValidatableObject.Number), null, s);
var validationMessage = lessThanOrEqualToValidator.ValidateProperty(context).FirstOrDefault();
AssertValidationMessage.NotEmptyMessage(validationMessage);
}