/// <summary>
/// Returns a <see cref="System.String" /> that represents this instance.
/// </summary>
/// <returns> A <see cref="System.String" /> that represents this instance. </returns>
public override string ToString()
{
var failed = Evaluations.OfType <FailedEvaluation>()
.Select(e => " " + e.ToString())
.Where(msg => !string.IsNullOrWhiteSpace(msg));
var passed = Evaluations.OfType <SuccessfulEvaluation>()
.Select(e => " " + e.ToString())
.Where(msg => !string.IsNullOrWhiteSpace(msg));
return
($"{Failures.Count()} failed (out of {Evaluations.Count()} evaluations)\n Failed:\n{string.Join(Environment.NewLine, failed)}\n Passed:\n{string.Join(Environment.NewLine, passed)}");
}