static void

BusinessValidationError

if(TestFails) Page.Validators.Add( new BusinessValidationError("Wrong input") );
Error message appears in the validation summary

using System.Web.UI;

///<summary>
///
An implementation of IValidator to enable server code messages to be added to a ValidationSummary
///</summary>
public class BusinessValidationError : IValidator
{
    ///<summary>
    ///Initializes a new instance of the <see cref="T:BusinessValidationError"/> class.
    ///</summary>
    ///<param name="errorMessage">The error message.</param>
    public BusinessValidationError(string errorMessage)
    {
        _ErrorMessage = errorMessage;
        _IsValid =
false;
    }

    #region IValidator
    
private string _ErrorMessage;
    
private bool _IsValid;

    
///<summary>
    /// Gets or sets the error message.
    ///</summary>
    ///<value>The error message.</value>
    string IValidator.ErrorMessage
    {
        
get { return _ErrorMessage; }
        
set { _ErrorMessage = value; }
    }

    
///<summary>
    /// When implemented by a class, gets or sets a value indicating whether the user-entered content in the specified control passes validation.
    ///</summary>
    ///<value></value>
    ///<returns>true if the content is valid; otherwise, false.</returns>
    bool IValidator.IsValid
    {
        
get { return _IsValid; }
        
set { _IsValid = value; }
    }

    
///<summary>
    /// When implemented by a class, evaluates the condition it checks and updates the <see cref="P:System.Web.UI.IValidator.IsValid"></see> property.
    ///</summary>
    void IValidator.Validate()
    {
    }
//Validate
    #endregion
}