Current date and time mocking

[Dmitry Butakov]

Hi,

Please help me to figure out how to mock functionality that's related to current time, date and so on. 

There should be a few classes that can check a possibility to get a discount according to their rules. 

For example there can be a class that gets a discount when current day of week is Sunday. Or when current time within predefined time frame.

I could create something like the following class hierarchy:

interface Matcher {

    int getDiscount();

}

class DayOfWeekMatcher implements Matcher {

    private DayOfWeek dayToBeMatched;

    private int discountValue;

    DayOfWeekMatcher(int discountValue, DayOfWeek dayToBeMatched) {

this.dayToBeMatched = dayToBeMatched;

this.discountValue = discountValue;

    }

    public int getDiscount() {

      // pseudo code

      return getCurrentDayOfWeek().equals(dayToBeMatched) ? discountValue : 0;

    }

 

    private DayOfWeek getCurrentDayOfWeek() {

// pseudo code

        return CURRENT_DOW;

    }

}

However there I see at least one problem, there is no way to set CURRENT_DOW outside the class. So the question is how to make getCurrentDayOfWeek be able to return "mocked" value? 

P.S. English isn't my native language, so if the problem's explanation isn't clear enough, please let me know.

Thanks,

Dmitriy

[Per Lundholm]

Hi
I think your English is just fine.
Don't know if this helps but I wrote about mocking the clock once.  There are some interesting comments to that post.
http://blog.crisp.se/2009/04/29/perlundholm/mock-the-clock

Cheers
Per

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[Juan Diego Hereñú]

You just can make a class that manages Time where you can ask now() instead of doing a new Date().

You have a collaborator to manage time, maybe you can add different methods if you need them like yesterday(), tomorrow() or just getCurrentDayOfTheWeek. Then you can just Stub that collaborator to get the day that you wish in your test.

interface Matcher {

    int getDiscount();

}

class DayOfWeekMatcher implements Matcher {

    private DayOfWeek dayToBeMatched;

    private int discountValue;

    private DateProvider dateProvider

    DayOfWeekMatcher(int discountValue, DayOfWeek dayToBeMatched, DateProvider dateProvider) {

this.dayToBeMatched = dayToBeMatched;

this.discountValue = discountValue;

        this.dateProvider = dateProvider;

    }

    public int getDiscount() {

      // pseudo code

      return getCurrentDayOfWeek().equals(dayToBeMatched) ? discountValue : 0;

    }

 

    private DayOfWeek getCurrentDayOfWeek() {

        return dateProvider.getCurrentDayOfTheWeek();

    }

}

Last week I read a post on ticking, it doesn't apply for your problem but is a good reading for the future:

http://java.dzone.com/articles/tdd-unit-tests-and-passage

Hope it helps.

JD

2013/12/16 Per Lundholm <per.lu...@gmail.com>

[Uncle Bob]

The other folks who have replied have done a good job of describing the solution.  I'll just add this:

Time is just another input to the system.  You should control that input the way you control every other input.  Do not couple to external time services (like the OS).  Instead, as you would for _any_ IO service, create your own interface to that service and use that interface exclusively.  This will allow you to mock out the time for any test context.