March 2018


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Robert Zupko <[log in to unmask]>
Reply To:
MASON Multiagent Simulation Toolkit <[log in to unmask]>
Thu, 15 Mar 2018 17:22:38 -0400
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This is a bit of idle speculation on my part, but having worked on a MASON
extension and another ABM at this point, I found myself either having to
use a dependency injection pattern or a singleton pattern so I could expose
objects that all of the agents eventually needed access to (e.g., random,
environmental attributes, etc.).

In terms of testing though, if SimState was hidden behind an interface
(e.g., ISimState) then you could use a mocking pattern and just initialize
the parts that are relevant to your test. From what I've seen of the MASON
code it might not be a major undertaking to make that change to the code

- Rob

On Thu, Mar 15, 2018 at 4:23 PM, Eric 'Siggy' Scott <[log in to unmask]> wrote:

> Simon,
> I can't speak to the actual rational behind SimState, but I can say that
> I've had similar frustrations in the past.  I do think that the "God
> object" approach is a bit easier for newcomers to learn.  It's easier to
> think in terms of an agent that "reaches out into the world and does stuff"
> than an agent that "is handed exactly what it needs and only what it needs
> as references at construction time, and works only with those references to
> affect the world" (which is the approach I naturally gravitate toward).
> But if you aren't careful, boy can it make unit testing frustrating!  To
> say nothing of tracking down weird unintended side effects.
> The solution I've settled on is to make sure that my "God object" can
> easily be partially initialized with only the components that are needed to
> provide indirect inputs and outputs to the agent under test.  This
> minimizes the need for stubbing and mocking, and arguably isn't any more
> difficult than testing an agent that takes references to data it needs at
> construction time.
> Siggy
> On Thu, Mar 15, 2018 at 11:28 AM, Simon Sohrt <
> [log in to unmask]> wrote:
>> I don't have a question about how to use some part of mason, but I am
>> rather curious about the reasoning behind the architecture of the interface
>> Steppable.
>> Why was the method step(SimState state) designed to take a parameter?
>> If my agents directly implement the interface Steppable, my agents have
>> access to all other objects in my simulation which makes my agents hard to
>> unit-test (since I have to initialize the 'god-object' SimState to call the
>> step-method).
>> I am aware that I can circumvent this by creating a Steppable as
>> described in the manual on page 109:
>> Steppable even = new Steppable() { public void step(SimState state) {
>>; }};
>> But isn't this a little bit ugly from a design perspective, because the
>> parameter state is completely ignored by
>> I am also aware that I can use the sim.engine.MethodStep-method to avoid
>> passing the SimState, but the manual does not recommend it for good reasons.
>> The manual also mentions that the Repast-method for stepping agents works
>> like the sim.engine.MethodStep-method from Mason, but I recently looked
>> into the current version of Repast Simphony 2.5 and Repast uses costume
>> annotations @ScheduledMethod(start = 1, interval = 1), to add methods to
>> the schedule, which seems to me that this is not a violation of Java
>> contracts (as the mason manual claims on page 108). Is the mason manual
>> maybe outdated or am I not correctly understanding the critique about the
>> way Repast schedules methods?
> --
> Ph.D student in Computer Science, George Mason University
> Web Director, Journal of Mason Graduate Research