Specification pattern

This code is base on Eric Evans and Martin Fowler's article introducing the Specification pattern

Simple example in the tests can be found here UserPreviouslyActiveIsPartOfTheRecentlyInactiveCohort.cs

ISpecification<UserContext> inactiveCohort =
                new UserIsInactiveForOverTwoWeeks()
                .And(new UserHasViewedSomeThing())
                .And(new UserHasUploadedSomeThing())
                .And(new UserHasNotReceivedAReportThisMonth());

var userContext = new UserContext
{
    LastActiveDate = DateTime.UtcNow.AddDays(-15),
    LastReportSent = DateTime.UtcNow.AddMonths(-1),
    TotalUploads = 10,
    TotalViews = 50
};

bool userInCohort = inactiveCohort.IsSatisfiedBy(userContext)

In this series

1. All about security
2. The power of Composite Specifications
3. Specifications 3: The DSL Strikes Back
4. Knock knock. Who's there? AbstractSpecificationNodeVisitorImpl