gistfile1.cs

[Fact]
public void TestSpecificationCollection()
{
    var minCredit = 3;
    var product = new Product() { MinimumCreditRating = minCredit, Price = 50 };
    var spec = new EligibleForDiscountSpecification(product);

    var customers = new List<Customer>()
                        {
                            new Customer() {CreditRating = minCredit-2}, // bad credit
                            new Customer() {CreditRating = minCredit-1}, // bad credit
                            new Customer() {CreditRating = minCredit} // good credit
                        };
    var eligible = from customer in customers
                   where spec.IsSatisfiedBy(customer)
                   select customer;

    Assert.True(eligible.All(c => c.CreditRating >= minCredit));
    Assert.Equal(1, eligible.Count());
}