Create Testing Behavior

To start let**'**s create a message from the Person agent that contains the basics - they’re requesting a test. In the check_infected behavior file, add a message function:

// check_infected.js

function check_hospital(state) {
  state.addMessage("Hospital", "test", {
    test_sick: true,
  });
}

You can add this function within the behavior function or above it.

If the person agent runs thecheck_hospital function, it will send a message to the agent named Hospital, with metadata of type test and a data packet that contains the boolean variable test_sick.

But we don't want our Person agent to be spamming the Hospital with requests to be tested - we only want to send it when the Person suspects that they are sick. We can add a property called time_to_symptoms in globals.json. That’s how long it takes for a person to start showing symptoms:

globals.json

 "time_to_symptoms" : 5,

We'll create a local variable to store the global global variable at the top of the check_infected behavior file, and add logic so it only sends a message after "symptoms" have developed:

// check_infected.js

function behavior(state, context) {
  const { time_to_symptoms } = context.globals();

  function check_hospital() {
    state.addMessage("Hospital", "test", {
      test_sick: true,
    });
  }

  if (state.infected && state.infection_length >= time_to_symptoms) {
    check_hospital();
  }
}

Now after a certain period of time the person agent will get suspicious they’re sick, and send a message to the hospital.

On the receiving end we need to add a message handler for the hospital. Create a new behavior file called test_for_virus. Add a message handler, so that every timestep an agent receives in its "mailbox" all the messages directed to its agent_id or agent_name:

// test_for_virus.js

function behavior(state, context) {
  const test_messages = context.messages().filter((m) => m.type === "test");
}

Make sure to attach it to the Hospital. Since we know we'll always want the behavior associated with the hospital, add it to the agent definition.

{
    "template_name": "hospitals",
    "template_count": 1,
    "template_position": "center",
    "agent_name": "Hospital",
    "behaviors": ["test_for_virus.js"],
    "height": 4,
    "color": "blue",
    "type": "hospital"
  }

So what should we tell our patient? If the person is sick the test should detect that they are sick; right now the only time a person messages the hospital is if they’re sick, so testing will be easy!

Let's check all of the messages and respond to each person, letting them know they are in fact sick. Add this snippet within the behavior.

// test_for_virus.js

test_messages.forEach((m) =>
  state.addMessage(m.from, "test_result", {
    sick: true,
  }),
);

Back in check_infected , we similarly want to check for any messages about our tests.

let msgs = context.messages().filter(msg => msg.type === "test_result");
msgs.forEach(msg => {
     if (msg.data.sick) {
     //do something
       break;
     }
    })

Now that our agent knows it’s sick, what should we do? When you’re sick, you should stay home and rest. So should our Person agents.

The daily_movement behavior contains our agent's movement logic. Importantly, we can have a Person go to a new destination by setting state.set("destination", state.get("new_destination")) so long as the new_destination is one that it has a "location for". Select the create_people behavior. You can see we assign each Person agent a grocery or office as their go-to grocery or office, and we store the position as a property on the Person:

// Line 20
const grocery = random_choice(agents["groceries"]).position;
const office = random_choice(agents["offices"]).position;

const template = state.people_template;

  agents["people"].push({
    ...template,
    position: home.position,
    home: home.position,
    grocery,
    office,
    // ...
  }

We're going to need to add the hospital as a potential destination as well:

// Line 20
const grocery = random_choice(agents["groceries"]).position;
const office = random_choice(agents["offices"]).position;
const hospital = random_choice(agents["hospitals"]).position;

const template = state.people_template;

  agents["people"].push({
    ...template,
    position: home.position,
    home: home.position,
    grocery,
    office,
    hospital,
    // ...
  }

If we set state.destination = "hospital" the Person will head to the hospital (we'll need that in the future).

For now though in check_infected, you can set the destination as home.

let msgs = context.messages().filter((msg) => msg.type === "test_result");
msgs.forEach((msg) => {
  if (msg.data.sick) {
    state.destination = "home";
  }
});

Now our full check_infected behavior looks like this:

function behavior(state, context) {
  const { time_to_symptoms } = context.globals();

  function check_hospital() {
    state.addMessage("Hospital", "test", {
      test_sick: true,
    });
  }

  let msgs = context.messages().filter((msg) => msg.type === "test_result");
  msgs.forEach((msg) => {
    if (msg.data.sick) {
      state.destination = "home";
    }
  });

  if (state.infected && state.infection_length === time_to_symptoms) {
    check_hospital();
  }
}

Run the simulation - our people are now being socially conscious and going back home when they’re sick. Hooray for well-being!