public void Selection()
{
var criteria = (Expression<Func<int, bool>>)(x => x > 0);
var negatedSpec = new Proposition<int>(criteria);
Assert.That(negatedSpec.IsSatisfiedBy(1), Is.True);
Assert.That(negatedSpec.IsSatisfiedBy(0), Is.False);
Assert.That(negatedSpec.IsSatisfiedBy(-1), Is.False);
}
